ECU Objects

Overview

The ECU contains a number of “objects” that represent settings or measurements and have varying types (e.g. Tables or Maps).

An object in this sense just refers to any ’thing’ in the ECU that can be configured or viewed in GWv4.

Alternatively, an “ECU Object” could be viewed as a memory range in the ECU memory map, which may be a single bit, a byte, a word, or a larger array of items in memory.

Nomenclature

This table shows an approximate mapping between the terms used in GWv4 and the terms used in the XCP/A2L and Simulink® worlds.

Note that Options / Tables / Maps are allowed to be stored in non-calibration (i.e. volatile RAM) memory and the same goes for Simulink signals, which is why this mapping is only approximate.

Calibration vs Measurement Objects

Calibration objects are those that can be modified by the user and are stored permanently by the ECU in non-volatile memory. These values are usually read from the ECU once when connecting to it.

Measurement objects are generally read-only and used to display real-time feedback about the ECU’s operation. Measurements are read frequently from the ECU when visible in the user interface or if they are being used for PC logging. There are some exceptions to this for monitoring some specific ECU functions, such as whether or not there are changes to the calibration that have not been saved to non-volatile memory.

See Calibrations for more information on calibration files / non-volatile storage.

The ECU may be configured to log measurements in internal logging memory for later retrieval. This is useful for diagnosing problems that may not be visible in real-time and offers much more precise timing resolution than is possible when polling the ECU over a comms link.

Output Pins

Overview

For many functions, the physical output pins that the function is routed to is user-selectable via ‘Out’ options.

e.g. Out Oil Feed 1 or Out Oil Feed 1 PWM.

Inverting Outputs (Active Low)

Depending upon the electrical characteristics of the output pin, it may be necessary to invert the output signal.

To invert the sense of the output, use a negative value in the calibration for the output pin.

Output Pin Restrictions

Some output pins have different features and restrictions. For example, some pins may be used for PWM outputs, digital outputs, or timed.

Care should be taken to ensure that multiple functions are not assigned to the same output pin as this would cause conflicts and un-defined behaviour.

The correct type of pin should be selected for the function being controlled, for example Out Oil Feed 1 PWM must be a PWM-capable output pin.

Pin Numbering

Refer to the ECU manual for the pin numbering scheme used by the ECU. The internal ECU pin numbering scheme differs to the physical pin numbering on the ECU connector.

ECU Internal Routing

Overview

Some functions may be configured / linked within the ECU using internal data / channel routing.

For example, the EGT (Exhaust Gas Temperature) sensor may be connected to any input channel, be it a physical analog input or from a CAN message.

Other features are more fixed, such as AIT (Air Intake Temperature) which only allows selection from a list of analog inputs.

Routing Options

Route-able features will typically have a ‘Source’ option that allows the user to select the input channel. The raw value of the input channel is displayed by a corresponding ‘raw’ channel.

For example, the Oil Feed 1 feature has an Oil Feed 1 Source option that selects the input channel for varying the duty cycle. The MSB of the raw input value is displayed by the Oil Feed 1 raw channel.

Source options often have a ‘Bigend’ option that specifies the upper/lower byte of the input channel, if it is 16bit. This is usually set to OFF. In some cases (e.g. Little Endian data coming via CAN bus) the bytes of the raw input channel may require swapping.

If the Bigend option is OFF then the MSB of the raw input value is displayed by the raw channel.

Routing via a User Table or User Map

ECUs will often provide some general purpose ‘User’ tables or maps that can be used for non-linear scaling from abitrary input data.

For example, the User 1 Duty table can be used to convert a raw input value to a ’tunable’ output value.

These tables and maps can be utilized by using intermediate routing steps.

flowchart LR
    CRX["CAN1 RX1 W1"]-->U1S["User1 Source"]
    U1S-->U1RAW(["User1 raw"])
    U1RAW-->U1DT["User1 Duty Table"]
    U1DT-->U1D(["User1 Duty"])
    U1D-->OF1S["Oil Feed 1 Source"]

Routing from CAN

Specific CAN messages may be received using the CAN Rx setup (from menu action CAN Rx Setup…) or via CAN RX related options in the calibration.

When the CAN port and CAN RX IDs are configured, the ECU will decompose the CAN message into 4x 16bit channels, e.g. for Message 1 on CAN port 1, the channels are:

CAN1 RX1 W1
CAN1 RX1 W2
CAN1 RX1 W3
CAN1 RX1 W4

CAN Routing Example (EGT)

If, for example, an external temperature sensor module is used that sends a CAN message to the ECU containing a reading for EGT, then this message could be assigned to a CAN RX message ‘box’ e.g. CAN1 RX1. If the EGT temperature was given in the first 2 bytes then CAN1 RX1 W1 would hold the EGT temperature value, in unscaled form.

To link up CAN1 RX1 W1 to the EGT feature, the EGT Source would be set to CAN1 RX1 W1.

If the received EGT signal is in Little Endian (Intel) format, then the EGT Source Bigend would be set to ON to swap the bytes.

The resulting raw value is displayed by the EGT raw channel and converted to voltage 0…5V for the full-scale input value. This is generally fine for A2D sources but in the case of data received by CAN, this is unlikely to be the correct interpretation. The EGT Sensor table should arrange to convert from these pseudo-volts to valid temperature.

For this example, the temperature module reports temperatures as signed 16bit numbers with 0.1°C resolution per bit. This poses a problem since EGT raw is unsigned and there is no way to make the source be interpreted as a signed number directly.

The EGT Sensor table would need to convert the signed number to an unsigned one by having a discontinuity. Note that hexadecimal values can be directly entered into the table cells (including the axis for many tables, like EGT Sensor).

This table shows the conversion from the EGT raw channel to a temperature in °C. Notice the discontinuity at 0x8000, which is the point where the signed number changes from full-scale positive to full-scale negative:

However, the EGT Sensor only supports positive output values, from 0 to 1275°C, depending on the value of the Temp Scalar option. See User Scalars for more details on the purpose / effect of scaling factors like Temp Scalar.

If there are 8 cells in the EGT Sensor table, the following values could be used, assuming that the Temp Scalar option = 1 (or 0, in which case the scalar is ignored) and that GWv4 is configured to display temperatures in units of degrees:

CAN Routing for Simulink® based ECUs

For ECUs that use a Simulink® model, CAN signals may be decoded from a DBC file. The messages are defined ahead of time as part of the firmware build process, the channels in the DBC file become available for use in the Simulink model as Simulink signals.

User Scalars

Overview

User Scalars are a feature that allows the units of values to be changed. ‘Option User Scalars’ also reference calibration options for to apply configurable scaling factors.

Scaling options e.g. like Temp Scalar are stored by the ECU but are not directly involved in any of the ECU’s internal calculations.

Purpose

Internally the ECU works with (typically) raw integer or ‘fixed point’ integer values (variables), and less commonly with floating point values. ECUs running Simulink® models are more likely to be using floating point numbers internally.

As far as the ECU is concerned, any quantities (temperatures, pressures, speeds, oxygen concentrations etc) are just numbers and the units are generally not important. The relationship between values, however, is important and additionally that related quantities use the same internal scaling.

Since integers are discrete values, there is a limit to how precisely values can be represented. The ECU may be able to offer more precise control if important quantities are scaled to make the best possible use of the available range of variables that represent them.

Consider an ECU table that contains 8 bit values; there are only 256 possible states / steps in each cell of the table. If the maximum expected range of physical values can be mapped to fit onto this 0…255 range, then the ECU can make the most precise control decisions. The scaling options, therefore, are telling GWv4 how to convert from these internal raw values into physical units. In other words, the ECU is using a custom type of units and the scaling options are defining how those custom units correspond to a physical ‘real-world’ unit.

For example, Temp Scalar is used as a scaling factor for a number of temperature values in the GWv4 user interface. The scaling is purely for display purposes - but it can mean that higher resolution temperature values can be used internally by the ECU. The units may also be further converted from °C by GWv4 to a different unit (e.g. °F) for display purposes - see Unit configuration.

Internally, the ECU does not care what the units are, just that values represent ratios for control purposes. Changing the units displayed in GWv4 does not change the internal operation of the ECU whatsoever.

Many tables and maps are preconfigured with sensible scaling factors and may not offer the ability to change them, where the level of precision is not so critical or where the range of input values is predictable.

Configuration

If an item is scaled using an Option User Scalar, this will be apparent in the Descriptions View. There may be a ‘Scalar’ (multiplier) option and/or an ‘Offset’ (signed addition) option.

For example, the Engine Load channel is scaled using the Load Scalar and Load Offset options.

These same scaling factors are used anywhere that raw Engine Load channel values might be encountered so that GWv4 will display them all correctly and the ECU can compare them consistently.

For example, the Fuel map might use the Engine Load channel as the input to one of its axes, and the RPM channel as the other axis. The load axis breakpoints may be configured, giving a non-linear axis to give more precise control at some points in the engine’s operating range.

The ECU will compare raw Engine Load values to the (raw) breakpoints in the Fuel map, and interpolate between them to find the correct fueling value. The ECU does not care what the actual units are - it is only operating on the raw integer values that represent the engine load. The GWv4 software will use the Load Scalar and Load Offset options so that the load values can be presented on screen in meaningful units.

Analog Outputs

Overview

The ECU has a number of Analog to Digital Converter (ADC) inputs that can be used to measure analog signals. These inputs may be assigned to different functions by setting options in the calibration.

Software Selectable Pull-up/Pull-down Resistors

Some channels have software selectable pull-up or pull-down resistors. These can be used to bias the input voltage to a known level when the input is not connected. This can be useful for sensors that do not have a built-in pull-up or pull-down resistor.

There are typically 2 options to control the pull-up or pull-down resistor. For example, the following table shows the options for Analog 10:

A10 Pull	T1 Pull High	Description
Off	Off	No pull-up or pull-down resistor (floating)
Off	On	No pull-up or pull-down resistor (floating)
On	Off	Pull-down resistor enabled
On	On	Pull-up resistor enabled

Some of the timing inputs have a pull-up resistor that can be enabled or disabled. Often the timing input would also have a fixed higher value pull-down resistor.

For example, the following table shows the options for T1 on a typical ECU:

T1 Pull-up	Description
Off	10k Pull-Down (used with VR sensor)
On	1k Pull-Up (used with Hall sensor)

Internal Switches

Overview

Input from various sources can be used to generate digital ‘switch’ (on/off) channels by a variety of methods. These internal switch channels may be selected numerically to control various functions in the calibration.

Some switches may be configured to come from external sources, such as CAN messages or digital input pins.

Comparator Switches

Timed Switches

Table Lookup Switches

Switch A.

Generic Switches

Switches selected from user source (e.g. CAN).

Load Sensing

Overview

The Engine Load may be measured in a variety of ways, such as using a Manifold Absolute Pressure (MAP) sensor (Boost Pressure), a Mass Air Flow (MAF) sensor, or a Throttle Position Sensor (TPS). Pedal position may also be used.

MAP or MAF may use Pedal as a backup should the primary sensor fail.

Scaling

The Load Scalar is used to convert the raw ’load’ values into more meaningful physical units.

Pedal as Load

If Fuel Map Pedal is On, then a correction, Boost Correction from the Boost Correct table is used to correct for the change in air pressure entering the engine.

This can result in a more responsive Pedal.

Note the Fuel Pedal map is used instead of Fuel map as the base fuelling in this case.

MAF Sensor

Overview

The Mass Air Flow (MAF) sensor measures the mass of air entering the engine. This may optionally be used to calculate the amount of fuel required to maintain the desired air/fuel ratio.

The MAF sensor is typically a hot wire or hot film sensor, which heats a wire or film to a constant temperature and measures the cooling effect of the air flow. The cooling effect is proportional to the mass of air flowing past the sensor.

The voltage output of the MAF sensor is often non-linear, so the ECU may apply a calibration curve to convert the raw voltage into a more useful linearized form.

MAF Sensor Options

Option	Description
MAF	Use MAF as the “Engine Load” measurement?
MAP	Set to 0 if using MAF for Engine Load.
Load source	Do not set if using MAF for Engine Load.
MAF source	Select an input channel to use for MAF. This could be an Analogue input or another source such as CAN bus.
MAF source Bigend	Swaps the bytes from the 16bit MAF source. This may be required if the source is from a little-endian (Intel) 16bit CAN signal.
MAF Raw	Raw MAF sensor reading as obtained from the MAF source.
MAF no Speed comp	If ON, the MAF sensor reading is not compensated for engine speed. Otherwise, the MAF sensor reading is multiplied by the inverse engine speed and divided down.
MAF no X16	If ON, the MAF sensor reading is not multiplied by 16, following speed compensation. This option does nothing if MAF no Speed comp is ON.
MAF Sensor	MAF Sensor Table to convert raw MAF sensor voltage into a linearized form.
MAF Cal	Number of internal teeth over which to average the MAF sensor readings when running. Typically this would be set to 1, 2 or 3 revolutions; the actual value to set here would depend upon the number of internal teeth per revolution which should be configured in the Wheel Teeth option.
MAF min	Minimum MAF sensor reading, below which an error condition is indicated.
MAF max	Maximum MAF sensor reading, above which an error condition is indicated.
MAF Linear	Linearized MAF reading, scaled using MAF (Load) Scalar.
MAF Linear Scaled	Linearized MAF reading, scaled using MAF Scalar.
MAF as Load	Compensated MAF reading, scaled using MAF (Load) Scalar.
MAF as Load Scaled	Compensated MAF reading, scaled using MAF Scalar.
Error MAF	Indicates an error condition with the MAF sensor.

Flowchart

flowchart TD
    MAFMIN@{ shape: diamond, label: "< MAF Min"}

    MAFMAX@{ shape: diamond, label: "> MAF Max"}
    MAFNSPD@{ shape: diamond, label: "MAF no Speed comp"}
    NOMAFMUL@{ shape: diamond, label: "MAF no X16"}

    MAFRAW["MAF Raw"]

    MAF_Source(["MAF source"])-- RUNNING? -->MAFSMP(["MAF samples"])
    MAFSMP-->MAFAVG["Average"]-->MAFRAW
    MAFCAL(["MAF Cal [teeth]"])--"Window Size"-->MAFAVG
    MAF_Source--"NOT RUNNING"-->MAFRAW

    MAFRAW-->MAFMIN
    MAFMIN-- Y -->ERROR_MAF(["Error MAF"])
    MAFMIN-- N -->MAFMAX

    MAFMAX-- Y -->ERROR_MAF(["Error MAF"])
    MAFMAX-- N -->MAFTBLW["MAF Sensor Table"]
    SPEEDN(["− Engine Speed"])
    MAFTBLW-->MAFLIN(["MAF Linear [MAF Load Units]"])
    MAFLIN-->MAFLINSCALED(["MAF Linear Scaled [MAF Units]"])
    

    MAFLIN-->MAFNSPD
    MAFNSPD-- N -->SPEEDMUL["×"]
    MAFNSPD-- Y -->MAFLOAD
    SPEEDN-->SPEEDMUL

    SPEEDMUL-->NOMAFMUL

    NOMAFMUL-- N -->MUL16["×16"]
    NOMAFMUL-- Y -->MAFLOAD
    MUL16--> Overflow -->ERROR_MAF
    MUL16-->MAFLOAD

    MAFLOAD(["MAF as Load [MAF (Load)]"])

    MAFLOAD-- "MAF AND NOT MAP AND NOT "Load Source"" -->LOAD(["Engine Load [Load]"])
    MAFLOAD-->MAFLOAD_SCALED(["MAF as Load Scaled [MAF Units]"])

MAP Sensor

Overview

MAP sensors measure the pressure of air entering an engine (Manifold Absolute Pressure). This information may be used by the ECU to calculate the amount of fuel required for combustion.

There are typically two MAP sensor inputs on the ECU, with the two sensors being used for redundancy and error checking.

The voltage output of the MAP sensor is typically linear with pressure, and the ECU can be configured to convert this voltage into a pressure reading in kPa.

The MAP sensor can optionally be used as a measure of Engine Load, in which case the ECU will convert the pressure reading into a load value. This load value is used as an axis input for many of the ECU’s calibration tables such as the Fuel map or the Ignition map.

Calibration

Option / Channel	Description
MAP	Use MAP as the “Engine Load” measurement?
MAF	Set to 0 if using MAP for Engine Load.
Load source	Do not set if using MAP for Engine Load.
MAP Source	The source of the MAP sensor data. This is an analog input number.
MAP2 Source	The source of the 2nd MAP sensor data. This is an analog input number. If using a single MAP sensor, MAP2 Source should be set to the same value as MAP Source
MAP Cal	Number of internal teeth over which to average the MAP sensor readings when running. Typically this would be set to 1, 2 or 3 revolutions; the actual value to set here would depend upon the number of internal teeth per revolution which should be configured in the Wheel Teeth option.
MAP1 samples	When running this table is filled with the samples used for averaging MAP1.
MAP2 samples	When running this table is filled with the samples used for averaging MAP2.
MAP raw Invert	Inverts the MAP sensor reading, useful for some sensors that output a voltage that decreases with pressure. This same setting applies to both MAP sensor inputs.
MAP1 raw	Result of averaging / inverting the MAP sensor voltage readings. This value can be monitored to verify the MAP sensor input configuration and that the analogue input is reading the MAP sensor correctly.
MAP2 raw	Result of averaging / inverting the second MAP sensor voltage readings. This value can be monitored to verify the MAP sensor input configuration and that the analogue input is reading the MAP sensor correctly.
MAP Min Error	The minimum valid voltage for the MAP sensor. If MAP raw reads below this value, an error will be triggered Error MAP. If MAP2 raw reads below this value, an error will be triggered Error MAP2.
MAP Max Error	The maximum valid voltage for the MAP sensor. If MAP raw reads above this value, an error will be triggered Error MAP. If MAP2 raw reads above this value, an error will be triggered Error MAP2.
MAP ref low Volts	The voltage output of the MAP sensor at a low pressure reference value MAP ref low Pressure.
MAP ref low Pressure	The physical pressure reading from the MAP sensor when the voltage reading from the analogue input reads MAP ref low Volts.
MAP ref high Volts	The voltage output of the MAP sensor at a high pressure reference value MAP ref high Pressure.
MAP ref high Pressure	The physical pressure reading from the MAP sensor when the voltage reading from the analogue input reads MAP ref high Volts.
MAP Pressure Max	If non-zero, this overrides the calculated MAP for Load Max for re-scaling MAP.
MAPM	The MAP sensor calibration multiplier, derived from the reference low and high pressure and voltage values.
MAPC	The MAP sensor calibration constant, derived from the reference low and high pressure and voltage values.
MAP for Load Max	Indicates the maximum pressure that the MAP sensor can read. This value is used to scale the MAP sensor readings to a load value.
MAP for Load Scalar	Alias of MAP for Load Max
MAP1 abs	The absolute value of the MAP sensor reading, in kPa.
MAP1 abs FP	The absolute value of the MAP sensor reading, scaled using Fuel Pressure Scalar.
MAP2 abs	The absolute value of the second MAP sensor reading, in kPa.
MAP2 abs FP	The absolute value of the second MAP sensor reading, scaled using Fuel Pressure Scalar.
MAP abs Peak	Maximum of MAP1 abs or MAP2 abs, in kPa.
MAP abs Peak FP	Maximum of MAP1 abs or MAP2 abs, scaled using Fuel Pressure Scalar.
MAP1 as Load	MAP abs is rescaled by the ECU to make more use of the full-scale range. Scaled to physical units using Load Scalar.
MAP2 as Load	MAP2 abs is rescaled by the ECU to make more use of the full-scale range. Scaled to physical units using Load Scalar.
MAP1-MAP2	The difference between MAP1 as Load and MAP2 as Load.
MAP1+MAP2/2	The average of MAP1 as Load and MAP2 as Load.
MAP as Load	The average of MAP1 as Load and MAP2 as Load, unless an error is detected (e.g. out of range voltage) in either input, in which case the valid input value is used where possible.
Engine Load	If the ECU is configured to use MAP as the measurement of Engine Load, this channel will show the value of MAP as Load. This value is scaled to physical units using Load Scalar, as with MAP as Load.
Error MAP	Error flag for MAP sensor 1. Set if the voltage reading is outside the range defined by MAP Min Error and MAP Max Error.
Error MAP2	Error flag for MAP sensor 2. Set if the voltage reading is outside the range defined by MAP Min Error and MAP Max Error.
Barometer	The barometric pressure reading, in kPa.
Boost1 gauge	The difference between MAP1 abs and Barometer, in kPa.

MAP as Load Scaling

The MAP1 abs value is rescaled to make full use of the range. This may therefore require adjustment to the Load Scalar to arrive at correct pressure values for MAP as Load and Engine Load.

Be aware that if the MAP sensor is not being used as a measure of Engine Load then the Load Scalar could be in use by something else. For example, if Load source is being used for Engine Load then the Load scalar may be responsible for rescaling the data selected by Load source so that Engine Load is in the correct units.

Flowchart

flowchart TD
    MAPMINER@{ shape: diamond, label: "< MAP Min Error"}

    MAPMAXER@{ shape: diamond, label: "> MAP Max Error"}
    MLDMAX_D@{ shape: diamond, label: "> MAP for Load max"}

    BARSCLD(["Barometer"])
    MAP1_abs(["MAP1 abs"])

    MAP_Source(["MAP Source (A2D)"])-- RUNNING? -->MAP1SMP(["MAP1  samples"])
    MAP1SMP-->MAP1AVG["Average"]-->MAP_raw_Invert
    MAPCAL(["MAP Cal [teeth]"])--"Window Size"-->MAP1AVG
    MAP_Source--"NOT RUNNING"-->MAP_raw_Invert["MAP raw Invert?"]
    MAP_raw_Invert-->MAPRAW1(["MAP1 raw [V]"])
    MAPRAW1-->MAPMINER
    MAPMINER-- Y -->ERROR_MAP(["Error MAP"])
    MAPMINER-- Y -->MAP_ZERO["0"]-->MAP1_abs(["MAP1 abs"])

    MAPMINER-- N -->MAPMAXER

    MAPMAXER-- Y -->ERROR_MAP(["Error MAP"])
    MAPMAXER-- Y -->MAP_FULL["MAX"]-->MAP1_abs(["MAP1 abs"])
    MAPMAXER-- N -->MAP1M["×"]
    MAPM-->MAP1M
    MAP1M-->MAP1C["+"]
    MAPC-->MAP1C
    MAP1C-->MAP1_abs

    MAP1M_SRC["(MAP ref high Pressure − MAP ref low Pressure) / (MAP ref high Volts − MAP ref low Volts)"]
    MAP1M_SRC-->MAPM(["MAPM"])

    MAP_Ref_low_v["MAP ref low Volts"]-->MAPC_M["×"]
    MAPM-->MAPC_M

    MAP_Ref_low_p["MAP ref low Pressure"]-->MAPC_C["−"]
    MAPC_M-->MAPC_C
    MAPC_C-->MAPC(["MAPC"])

    MAPC-->MLDMAX_ADD["+"]
    MAPM-->MLDMAX_ADD["+"]
    MLDMAX_ADD-->MLDMAX(["MAP for Load Max [kPa]"])
    MLDMAX_ADD-->MLDS(["MAP for Load Scalar"])

    MLDMAX-->MLDMAX_D
    MLDMAX-->MAP1_abs_DIV

    BARSCLD-->MAP1_abs_sub
    MAP1_abs-->MAP1_abs_sub["−"]

    MAP1_abs_sub-->BSTGAGE1["Boost1 gauge"]

    MAP1_abs-->MLDMAX_D
    MLDMAX_D-- Y -->MAP1_abs_FULL["MAX"]-->MAPLOAD1(["MAP1 as Load [Load]"])
    MLDMAX_D-- N -->MAP1_abs_DIV["/ MAP for Load max"]-->MAPLOAD1(["MAP1 as Load [Load]"])

    MAPLOAD1-->MAPLOAD1_MINUS_2
    MAPLOAD2(["MAP2 as Load [Load]"])-->MAPLOAD1_MINUS_2

    MAPLOAD1_MINUS_2["−"]-->MAPLDIFF(["MAP1-MAP2 [Load]"])

    MAPLOAD1-->MAPLOAD1_AVG_2
    MAPLOAD2-->MAPLOAD1_AVG_2
    MAPLOAD1_AVG_2["Average OR Select"]-->MAPLDAV(["MAP1+MAP2/2 [Load]"])
    MAPLOAD1_AVG_2-->MAPLOAD(["MAP as Load [Load]"])

    MAPLOAD-- "MAP AND NOT MAF AND NOT "Load Source"" -->LOAD(["Engine Load [Load]"])

Digital Outputs

Overview

The ECU has a number of digital outputs (ON / OFF) that can be used to control various devices through the wiring loom. These outputs may be assigned to different functions by setting options in the calibration.

Some digital outputs may be switched to other functions such as PWM or timed outputs. For devices that require a proportional control signal, use a PWM output channel instead.

PWM Outputs

Overview

The ECU has a number of Pulse Width Modulated (PWM) outputs that can be used to control various devices. These outputs may be assigned to different functions such as VV control, Idle valve, Wastegate, Servo.

Some PWM outputs may be claimed by specific functions. For instance, if Active Throttle is enabled, it owns a bridge driver and prevents others attempting to use the output, unless e.g. Act T 1 No Drive is set to ON.

Duty Cycle

The duty cycle of a PWM signal is the ratio of the ‘on’ time to the total period of the signal. The frequency of the PWM signal is the rate at which the signal repeats. Over time, this produces a proportional control signal with low power loss.

For devices that require a simple on/off control signal, use a digital output channel instead.

Configuration

PWM outputs must be enabled using options in the calibration and are typically routed to from ECU functions using additional calibration options.

Some PWM outputs are used for specific features such as active throttle, so some care is required to avoid conflicts.

Restrictions

PWM1-16 are fixed to individual pins, however, PWM17 onwards are assignable to any simple output pin. In the pin-outs diagram/table, these fixed PWMs have a code of ‘Pnn’, where ‘nn’ is 01-16.

PWM Output Pin Assignment

For PWMs that may be assigned to output pins, pin assignment options are available in the calibration.

e.g. Out PWM17

As with any other output pin assignment, using a negative value will invert the output signal.

Oil Feeds

See Oil Feed Outputs for details on the Oil Feed channels - which can either use PWM outputs or generate low-speed PWMs in software on simple digital outputs.

Timed Outputs

Overview

Timed output pins are used for precisely timed pulses for functions such as Ignition, Injection, High Pressure Pump, etc.

On the EM80, there 8 x 8bit PWM output pins that can be PWM outputs 1 to 8, injector outputs 1 to 8 or simple low-side outputs.

Timed outputs allow the processor to schedule asynchronous events like ignition in response to crank tooth interrupts, with high precision timing and are enable features like variable ignition advance / retard to work.

Oil Feed Outputs

Overview

GEMS ECUs typically provide 4 Oil Feed output controllers for controlling solenoid pumps. This section discusses Oil Feed 1, but the same principles apply to the other Oil Feed output controllers.

It is recommended that the behaviour of the oil outputs is tested following configuration. Monitoring the associated output pin channel using a Scope View or a physical oscilloscope is recommended.

Oil Feed Configuration

Each oil feed controller has a set of configuration options. Considering Oil Feed 1:

Option	Description
Oil Feed 1 Source	Selects an input channel for varying the duty cycle. The MSB of the raw input value is displayed by the Oil Feed 1 raw channel.
Oil Feed 1 Source Bigend	Specifies upper/lower byte of the input channel, if it is 16bit. This is usually set to OFF. In some cases (e.g. Little Endian data coming via CAN bus) the bytes of the raw input channel may require swapping.
Oil Feed 1 Mul	Multiplier for re-scaling the raw input value, saturates at 100% duty cycle in case of overflow. The result is stored in Oil Feed 1 Duty
Oil Feed 1 PWM Out Out Oil Feed 1 PWM	PWM channel number for high rate / precision PWM, using PWM output settings with duty cycle Oil Feed 1 Duty. Note: PWM numbers are not the same as output pin numbers.
Oil Feed 1 Out Out Oil Feed 1	Digital output pin for low rate PWM, only used if Oil Feed 1 PWM Out = 0. If a negative value is supplied for the pin number here (e.g. ‘-5’), the signal is inverted (on e.g. pin ‘5’). In this case there are additional Oil Feed options to control the software PWM.

Digital Output Configuration

If the Oil Feed output is using a digital output instead of a PWM output, a low frequency / low precision PWM is generated by software.

The following common options are effective in this mode:

Option	Description
Oil Feed 1 Stop Duty	If ON then when Stat Running is OFF, Oil Feed 1 Duty Stopped will be used for the duty cycle of the output, unless Oil Feed 1 Stopped OFF is ON (in which case the output would be switched ‘OFF’).
Oil Feed 1 Duty Stopped	Duty cycle to use when engine is not running (Stat Running is OFF), depending upon Oil Feed 1 Stop Duty and Oil Feed 1 Stopped OFF options
Oil Feed 1 Fixed On	Use a fixed-length ON pulse, with the duty cycle affecting the duration of the space between ON pulses.
Oil Feed 1 Stopped OFF	If ON then the output will be switched off when the engine is not running (Stat Running is OFF), otherwise the output will be set to Oil Feed 1 Duty Stopped.

Fixed Mode

Enabled when Oil Feed 1 Fixed On = ON.

This mode uses a fixed duration ON pulse and variable duration OFF interval.

Option	Description
Oil Feed 1 Fixed On	ON
Oil Feed 1 Fixed T.B.	Maximum duration of variable part of OFF period, in milliseconds (added to Oil Feed 1 OFF min).
Oil Feed 1 Fixed comp	If set, changes the type of complement operation performed on Oil Feed 1 Duty prior to scaling Oil Feed 1 Fixed T.B.. If ON then a 1’s complement (logical NOT) is used instead of 2’s complement (arithmetic negation). It is recommended to set this to ON for new calibrations and can give better results at higher frequencies.
Oil Feed 1 OFF min	Minimum duration of OFF period, in milliseconds.
Oil Feed 1 Fixed ON Duty	Fixed duration of ON pulse, in milliseconds.
Oil Feed 1 Period	Reports current period of signal.
Oil Feed 1 T Count	Count-up timer, used for signal generation.

The duration of the ‘OFF’ interval is calculated by scaling option Oil Feed 1 Fixed T.B. by the (inverted) duty cycle percentage shown by Oil Feed 1 Duty.

The OFF interval can’t ever be 0 and will have a lower limit of 1ms. The lower limit may be clamped to a higher value by setting the Oil Feed 1 OFF min option.

Oil Feed 1 Fixed ON Duty option defines the duration of the ON pulse. This added to the calculated OFF duration to give the total period of the PWM signal and is placed in Oil Feed 1 Period.

Oil Feed 1 T Count counts up every millisecond.

When Oil Feed 1 T Count exceeds the value of Oil Feed 1 Period, the output is switched on and Oil Feed 1 T Count is reset to 0.

When Oil Feed 1 T Count reaches Oil Feed 1 Fixed ON Duty, the output is switched off.

Proportional Mode

Enabled when Oil Feed 1 Fixed On = OFF.

Proportional mode has a fixed period and varies the duty cycle of the signal over that period. Additionally this mode can limit the total number of pulses delivered to the output after ECU reset.

Option	Description
Oil Feed 1 Fixed On	OFF
Oil Feed 1 Duty Max	Maximum ON period
Oil Feed 1 Fixed comp	If set, changes the type of complement operation performed on Oil Feed 1 Duty prior to scaling Oil Feed 1 Duty Max. If ON then a 1’s complement (logical NOT) is used instead of 2’s complement (arithmetic negation). It is recommended to set this to ON for new calibrations and can give better results at higher frequencies.
Oil Feed 1 Time base	Total period of the PWM signal, in milliseconds.
Oil Feed 1 P Max	Maximum number of pulses to deliver to the output before ECU reset. If 0, then no limit is applied.
Oil Feed 1 P Count	Reports the number of pulses delivered to the output when Oil Feed 1 P Max is non-zero.
Oil Feed 1 Duty Time	Stores the result of scaling Oil Feed 1 Duty Max by Oil Feed 1 Duty.
Oil Feed 1 T Count	Count-down timer, used for signal generation.

New calibrations may prefer to use Oil Feed 1 Fixed On = ON.

Oil Feed 1 T Count is decremented every millisecond. When Oil Feed 1 T Count reaches zero, the output is switched off.

When the output is switched off, Oil Feed 1 T Count is reset to Oil Feed 1 Time base. Additionally the result of scaling Oil Feed 1 Duty Max by Oil Feed 1 Duty is stored in Oil Feed 1 Duty Time. Note that this does not happen in ‘Fixed Mode’.

When Oil Feed 1 T Count reaches the value of Oil Feed 1 Duty Time, the output is switched ON.

When switching on the output, if Oil Feed 1 P Max option is non-zero then the Oil Feed 1 P Count will count up to this value, and the output will cease to be switched on again until the ECU is reset when Oil Feed 1 P Max pulses have been delivered to the output.

Mapped Control

The ECU provides user tables and maps that may be used to control the Oil Feed outputs.

See ECU Internal Routing for details on how to route these user maps to the Oil Feed outputs.

Peak & Hold Injector Outputs

Overview

Some GEMS ECUs provide dedicated on-board “Peak & Hold” injector outputs that provide a specially shaped pulse to drive injector solenoids.

Peak and Hold Injector Drive

Instead of a simple ON/OFF signal driving an injector solenoid, the drive transistor is first driven hard on for a specified time to ensure opening, then the current is dropped to a holding current, minimising heat dissipation in both injector and transistor. When the injector is closed, the driver circuit recirculates energy from the collapsing magnetic field of the injector coil, preventing abrupt closure of the injector which can lead to physical injector damage (fuel leakage) and unpredictable fuel delivery due to pintle bounce.

The peak & hold injectors are active if Injector Peak & Hold = ON.

Peak

The Injector Peak Time table specifies the time that the drive transistor is fully ON for, prior to entering hold mode. The peak time is dependent on battery voltage, since this directly affects the rate at which the magnetic field within the injector builds.

Some ECUs may include table Injector Peak Decay Time, which is currently unused, future versions may implement this as a smoother transition from peak to hold.

Hold

The frequency and duty of hold signal is given by option Injector Hold Frequency, and table Injector Hold Duty.

Recirculation

The recirculation diode is controlled per injector driver by options Fuel 1 Recirculate … Fuel 8 Recirculate. Recirculation manages the current flow when the injector is turned off to smooth the closing.

Compensations

Tables Injector Volts comp and Injector Volts comp Secondary allow for additional compensation in response to battery voltage changes.

Compensations are displayed by channels Injector Comp Fuel Primary and Injector Comp Fuel Secondary.

Fuel Pressure Scalar

Overview

The fuel pressure scalar is used to convert the raw fuel pressure values into more meaningful physical units.

By default, the fuel pressure scalar is calibrated to units of Bar, but this can be changed to other units of pressure - see Units.

Fuel Pressure Scalar Options

Option	Description
Fuel Pressure Scalar	Multiplier, m as in the linear scaling equation, y = mx + c.
Fuel Pressure Offset	Offset c as in the linear scaling equation, y = mx + c.

Load Scalar

Overview

The load scalar is used to convert the raw ’load’ values into more meaningful physical units.

Typically, Load values are pressure readings calibrated to units of kPa, but this can be changed to other units of pressure (or other quantities) - see Units.

Note that changing the load scalar will affect the meaning of any related calibration values and measurements collectively, which may require recalibration of the ECU.

For example, if using MAP as Load and the MAP sensor is changed to one with a different range, then all load related items may require recalibration if the scaling of raw MAP readings no longer leads to equivalent physical pressure values.

Load Scalar Options

Option	Description
Load Scalar	Multiplier, m as in the linear scaling equation, y = mx + c.
Load Offset	Offset c as in the linear scaling equation, y = mx + c.

MAF (Load) Scalar

Overview

The Mass Air Flow (MAF) scalar is used to convert raw flow measurement values into more meaningful physical units.

By default, the MAF scalar is calibrated to g/s, but this can be changed to other units of mass flow.

MAF (Load) Scalar Options

Option	Description
Load Scalar	Multiplier, m as in the linear scaling equation, y = mx + c.
Load Offset	Offset c as in the linear scaling equation, y = mx + c.

MAF Scalar

Overview

The Mass Air Flow (MAF) scalar is used to convert raw flow measurement values into more meaningful physical units.

By default, the MAF scalar is calibrated to g/s, but this can be changed to other units of mass flow.

MAF Scalar Options

Option	Description
MAF Scalar	Multiplier, m as in the linear scaling equation, y = mx + c.
MAF Offset	Offset c as in the linear scaling equation, y = mx + c.

RPM Pickup Wizard

Overview

A wizard is available for GWv4 that simplifies configuring the crankshaft / camshaft sensors and the computation of the engine cycle position and RPM.

If you have an unusual tooth pattern or sensor configuration, you may need to manually configure these settings. Contact GEMS for assistance if you are unsure.

There are also existing Calibration and Aspect files available for many common configurations.

• Start Maps and Setups
• Calibration Aspects

Crank Sensor

Overview

The crank sensor is used to determine the position of the crankshaft and the speed of the engine. The crank sensor is usually mounted on the engine block and reads a toothed wheel mounted on the crankshaft. It may be used in conjunction with a camshaft sensor to determine the position of the engine cycle.

Sensor Type

The crank sensor is usually a Hall effect sensor or a VR (Variable Reluctance) sensor. The sensor is connected to ECU timer T1 which has a software selectable pull-up resistor.

Sensor Type	T1 Pull-up
Hall Effect / Optical	Yes
VR / Inductive	No

Edge Selection

The ECU man be configured to select which edge of the signal is used to interrupt the ECU for engine position related processing, these options may be named differently on some ECUs:

• Crank Rising Edge or T1 Rising Edge
• Crank Falling Edge or T1 Falling Edge

VR sensors have one direction edge that is sharply defined. In the other direction, there are 2 edges and they are slower. Selecting the correct edge here is crucial to ensure accurate engine position detection.

    xychart-beta
    title "VR Sensor Pulse"
    x-axis [0, 1, 2, 3, 4, 5, 6, 7, 8]
    y-axis "Voltage" -5 --> 5
    line [0, 0, -0.3, -3, 3, 0.3, 0, 0, 0]

An oscilloscope can be used to determine the best edge to use. The sensor output should be monitored while running / turning over the engine to determine which edge is the most sharply defined.

To verify that the correct edge has been selected, it is recommended to record an ECU internal data log with the crankshaft moving at a constant rate. It is expected that the synchronization strategy and Tooth Control table have been configured before this test.

Channel	Description
A Tooth	Actual teeth feed into to Tooth Control table.
Wheel Tooth	Decoded internal tooth number, increments up to the value of Wheel Teeth.
Fuel Tooth No	Decoded internal teeth for engine cycle, decoded by Tooth Control table used for fuelling, increments up to the value of Fuel Teeth..
Ign Tooth No	Decoded internal teeth for engine cycle, decoded by Tooth Control table used for sparking, increments up to the value of Spark Teeth..
MX Tooth Time	Time interval between actual teeth; i.e. time separation between crank interrupts.
Tooth Time	Time interval between internal teeth decoded by Tooth Control table. The most important measurement in ECU.

The following images show the difference between the correct and incorrect edges for a VR sensor:

Incorrect Edge

See the long tooth interval detected in MX Tooth Time when A Tooth = 0

The long tooth appears to be in 2 parts of 3.296 and 1.482 ms, with the regular teeth spaced at 1.185 ms.

This is from a 30-2 wheel so the missing tooth interval should be approximately 3x the regular teeth interval.

Notice that the Tooth Time channel has major discontinuities; it is expected that the internal teeth (decoded by the tooth control table) are regularly spaced and so a more constant value is expected here.

Correct Edge

With the Crank Rising Edge and Crank Falling Edge swapped we get just a single long MX Tooth Time 3.754 ms, equal to 3 regular teeth (on a 30-2 wheel) as expected. The regular teeth are spaced at ~1.243 ms:

3.754ms / 1.243ms = 3.02 teeth

Also notice that the Tooth Time and A Tooth channels are smoother, meaning that the edges are interrupting the ECU more reliably.

If you are unable to start the engine and idle, it is possible to get the timing wheel running at a steady speed by removing the spark plugs (to avoid compression) and using the starter motor to turn the engine over. This will allow the ECU to log the crankshaft position data without the engine running. For safety, any injection and spark outputs can be disabled in the ECU calibration for this test.

Crankshaft Position Sensor Filtering

Hardware Filtering

• T1 Filter Below - RPM value below which the T1 filter is active.
• T1 Low Sens Above - Reduces the sensitivity of the T1 input above this RPM value, can be useful for VR sensors.
• Crank Filter - Time window, in microseconds, for filtering edges on the crank sensor input.

Software Filtering

• Tooth Short Ignore - Enables software filtering of short tooth intervals. This is useful for filtering out noise on the crank sensor input.
• Tooth Short Running - This is a percentage of the last valid actual tooth interval, edges detected that are less than this percentage are rejected.
• Tooth Short Start - When cranking (starting) the engine, before synchronization is achieved, Stat Sync'd == OFF, software filtering uses a fixed time interval for rejecting edges - edges detected that are less than this interval will be rejected.

When running, Tooth Time x Tooth Short running is used to determine the minimum tooth interval that will be considered a valid tooth event.

The calculated value for the short tooth test is stored in A Tooth Short Test.

If a short tooth is detected, it will record this information in:

• A Tooth Short [ms] - captures captures MX Tooth Time
• A Tooth Short No - captures A Tooth
• A Tooth Short Rev - captures Cam count MX

This information will be recorded regardless of whether Tooth Short Ignore is set.

Cam Sensor

Overview

A cam sensor is used to determine the position of the camshaft, typically relative to the Crank Sensor.

Camshaft Position Sensor

If a camshaft position sensor is required, similarly to the crank sensor, it is usually a Hall effect sensor or a VR (Variable Reluctance) sensor. The sensor is typically connected to ECU timer T2 which has a software selectable pull-up resistor. It is possible to use a different timer input if required but T2 is the most common choice.

Sensor Type	T2 Pull-up
Hall Effect / Optical	Yes
VR / Inductive	No

As with the crank sensor the cam synchronization edge should be configured.

If you are planning on using the VVC (Variable Valve Control) features then T2 should be configured for both edges, with the appropriate edge for Cam or 4 stroke cycle synchronization selected by the Sync channel T option. VVC control would require configuration with the other direction edge where appropriate (VVC1 source T, VVC2 source T, VVCX1 source T, or VVCX2 source T).

For example:

Option	Value
T2 Rising Edge	ON
T2 Falling Edge	ON
Sync channel T	“T2 Rise”

If not using T3-T12 timing inputs they can be switched off with T3 - T12 Disable to avoid any additional CPU overhead.

Camshaft Sensor Filtering

Like the crank sensor, the cam sensor can have hardware filtering applied to it:

• T2 Filter Below - RPM value below which the T2 filter is active.
• T2 Low Sens Above - Reduces the sensitivity of the T2 input above this RPM value, can be useful for VR sensors.

Engine Cycle Sync (Camshaft)

Overview

On 4 stroke engines where sequential injection and/or ignition is required, the ECU must synchronize to the correct revolution of the engine cycle so that the correct fuel and spark events are generated.

The crank wheel typically rotates once per revolution and therefore does not provide the ECU with enough information on its own.

However, the camshaft rotates once per cycle (2 revolutions of the crankshaft) and a sync signal from the camshaft can be used to determine the engine cycle.

Camshaft Sync

The ECU counts the occurrence of rising or falling (or both) edges from the cam sensor.

The counter, typically T2R counter (rising) or T2F counter (falling), is captured at an actual crank tooth Sync Test A Tooth and is reset to zero to begin counting again; the counter will be reset every crank revolution at the specified tooth.

Example:

In this example with a 8-1 crank wheel, there are 2 rising edges in the 1st crank revolution and 1 rising edge in the 2nd crank revolution.

The synchronization test point may be adjusted using the Sync Test A Tooth option.

Sync Test A Tooth is the actual crank tooth number (i.e. not an internal tooth number) at which the camshaft counter is captured and reset to zero on every crank revolution. The value is captured into the Cam Tooth Count channel.

Sync Teeth is the number of Cam teeth expected at Sync Test A Tooth when testing for synchronization if the engine is within the expected half of the 4-stroke cycle.

If Sync Test A Tooth were set to 6 in this example (corresponding to the 7th tooth of the crank wheel, counting from 0), then the counter would be set to 2 in the first revolution and 1 in the second revolution.

Setting Sync Teeth to 2 would result in synchronization to be achieved on the 1st crank revolution. If set to 1 then synchronization would be achieved on the 2nd crank revolution.

During the ‘synchronization’ portion of the tooth control table, the captured counter value is tested against the Sync Teeth value.

Variable Valve Control Systems

On variable cam control systems, the timing of the camshaft signal varies with respect to the crankshaft signal.

Considering the example diagram again, if the camshaft was in its most retarded position at that point then the ‘Cam’ signal could shift to the left by up to 80 degrees (almost 2 Actual Teeth in this example).

The original example with Sync Test A Tooth set to 6 would still be correct, when counting rising edges, for either cycle 1 or cycle 2 if the cam signal were shifted to the left by as far as 2 teeth.

However, suppose Sync Test A Tooth was set to 4. There would be multiple issues:

• In the first revolution, the ECU would detect either 1 or 2 teeth, depending on whether the camshaft position was advanced by VVC.
• In the second revolution, Sync Test A Tooth closely coincides with the cam signal, and there is a race between the crank signal and cam signal - small timing variations could cause unreliable detection of the cam signal.

In both cases, the cycle detection would be highly unreliable.

Edge Selection

Depending upon the cam sensor configuration, the ECU could be counting rising edges, falling edges or both.

The cam sensor edge direction may be selected by a combination of T2 Rising Edge, T2 Falling Edge and Sync Channel T.

It is possible to use timers other than T2 for cam synchronization, but T2 is the most common.

Engines with Variable Valve Control (VVC / VVT) would typically require both edges to be enabled with Sync Channel T set to either “T2 Rise” or “T2 Fall” so that only the rising or falling edge of the cam signal is used for engine cycle synchronization.

The edge selection may require adjustment to improve engine cycle detection.

If you are using a VR (Variable Reluctance) sensor for the Cam sensor then there may only be 1 valid edge due to the nature of signals from VR sensors - see Crank Sensor.

Sync 2 (Reliably Synchronize Within 1 Revolution)

An optional feature is available to support synchronization within a single crank revolution.

If Sync 2 Active is set to ON, then the cycle shall also be matched using Sync 2 Teeth.

If Cam Tooth Count matches Sync 2 Teeth then synchronization will be achieved (Stat Sync'd will be set to ON) and the value of Sync 2 Fuel Tooth will be placed into Fuel Tooth and the value of Sync 2 Spark Tooth will be placed into Spark Tooth to ‘jump’ these important clocks to the next half of the cycle.

Considering the example again:

For sequential injection + ignition with 4 internal teeth per revolution, this example ECU could be configured with:

Option	Value
Sync Teeth	2
Sync Test A Tooth	6
Sync 2 Active	ON
Sync 2 Teeth	1
Sync 2 Fuel Tooth	4
Sync 2 Spark Tooth	4
Fuel Teeth	8
Spark Teeth	8

Options / Channels

Option	Description
Start No Cam Sync	The ECU will not attempt to synchronize to the camshaft while cranking (starting) the engine.
Sync Channel T	Selects Cam synchronization input timer (e.g T2 Rise)
Sync Teeth	Number of teeth expected to unambiguously identify 1 revolution in the engine cycle. Must be set to 0 if not using a Cam Sync input.
Sync Test A Tooth	The actual crank tooth number at which the camshaft counter is captured and reset to zero. This is the actual crank tooth (A Tooth) number, not the internal tooth number. Care should be taken, particularly with systems using VVC, to ensure reliable detection across the range from most retarded to most advanced camshaft positions.
Cam Tooth Count	Value of the sync channel (e.g. T2R counter) when A Tooth reaches Sync Test A Tooth
Cam Tooth MX	Value of Cam Tooth Count when ‘MX’ (Missing / Extra tooth) synchronization tested.
Sync 2 Active	Enabled Sync 2 feature.
Sync 2 Teeth	Number of teeth to identify 2nd revolution in the engine cycle.
Sync 2 Fuel Tooth	Value to set in Fuel Tooth if Sync 2 is achieved. Jumps the injection ‘clock’ to the next half of the cycle. Should be set to the number of internal teeth per revolution, if sequential injection is required.
Sync 2 Spark Tooth	Value to set in Spark Tooth if Sync 2 is achieved. Jumps the ignition ‘clock’ to the next half of the cycle. Should be set to the number of internal teeth per revolution, if sequential ignition is required.

Actual Teeth vs Internal Teeth

Overview

There is a difference between actual teeth on the crankshaft wheel and internal teeth used by the ECU for triggering ignition or injection events.

Internal teeth always coincide with actual teeth but they are arranged such that they are at evenly spaced crank angles.

Actual Teeth vs Internal Teeth

Events from ‘actual teeth’ on the crankshaft wheel cause the ECU’s CPU to be interrupted. The ECU decides whether these events are ‘active edges’ aka ‘internal teeth’ that may be used for triggering ignition or injection events.

If using a missing / extra tooth strategy, the actual tooth events are not evenly spaced. The ECU is able to detect this un-even spacing to identify missing / extra teeth.

If the engine cycle can be determined from a camshaft sensor, and sequential injection or ignition is required, then the Fuel Teeth and Spark Teeth options should wither be set to the same value as the number of internal teeth (e.g. wasted spark) or to double the value (sequential).

Synchronization

Overview

Once the crank / cam sensors are configured, the synchronization strategy and tooth pattern must be set up to be able to synchronize the ECU with the engine.

When cranking / starting the engine, the ECU will initially be in an unsynchronized state. The ECU will not be able to determine the engine cycle position until synchronization is achieved.

When the ECU reaches the synchronized state, the Stat Sync'd channel will be set to ON.

During cranking, the ECU uses a different control strategy to normal running.

Synchronization Strategy

The most common synchronization strategy is to use a Missing tooth (or eXtra tooth) on the crankshaft wheel, GEMS ECUs refer to this as the Sync MX strategy.

There are 4 synchronization strategies available, controlled by 3 options. These options must be set in a mutually exclusive way:

• Sync MX - Missing / extra tooth/teeth on the crankshaft wheel.
• Sync Cam Count - Simplest strategy, uses the camshaft sensor to determine the engine cycle position, prefer Sync Crank S count if possible.
• Sync Crank S Count - Similar to Sync Cam Count, counts the number of crankshaft teeth between camshaft teeth.
• Sync Cam - when the above 3 options are OFF. Ignores the Tooth Control table and used camshaft signal to subdivide the engine cycle.

Tooth Control Table

Overview

The main goal of the Tooth Control table is to subdivide the physical timing wheel teeth (actual teeth) into regularly spaced internal teeth.

RPM Pickup Wizard

The RPM Pickup wizard can be used to calculate the Tooth Control table values, given some common timing wheel types.

Tooth Control Table

The Tooth Control table is a low-level ECU feature that is not obvious but essential to understand if needing to accommodate unusual tooth patterns.

Each site in the Tooth Control table corresponds to the sequence of ECU interrupts (events) from actual teeth passing the crank sensor and are therefore not necessarily evenly spaced in time or angle; there will not be any events in the missing section of the wheel or there may be an extra tooth. Some timing wheels have more than one missing teeth section.

The aim is to select from these events an evenly spaced real-world pattern of internal teeth that can be used to schedule fuelling and ignition events. The internal teeth are used to subdivide the engine cycle into equal parts, and the ECU will increment internal tooth counters for each internal tooth detected, with separate counters for fuelling and ignition.

If using a wheel with 2 missing teeth in a row, for example, then the actual teeth will need to be divided by at least 3 (possibly more) to ensure that no internal teeth fall within the missing section and are also evenly spaced in terms of crank angles. Each internal tooth must coincide with an actual tooth passing the sensor; i.e. an interrupt/event occurs in the ECU for each internal tooth.

It is common to subdivide the timing wheel into 12 internal teeth. For example, with a 36-2 wheel that has 2 missing teeth in a row this can be divided by 3 into 12 equally spaced internal teeth that all coincide with actual teeth.

When actual teeth are detected, the ECU will increment A Tooth and use the value to look up the corresponding site in the Tooth Control table.

Each value in the table is composed of 3 digital ‘bits’ (1/0):

Value	Bits	Function
0	000	Do nothing.
1	001	Active Edge (Internal Tooth).
2	010	Alternate Edge (Used for Crank Alt Fire mode).
3	011	Reset A Tooth, if loss of sync. Indicates the end of the table.
4	100	Test for synchronization.
5	101	Active Edge (Internal Tooth) + test for synchronization.
6	101	Alternate Edge + test for synchronization.
7	111	Reserved (do not use this value).

Unless all sites in the table are required, the value ‘3’ should be placed at the end of the table so that loss of synchronization can be detected; if A Tooth overruns the valid section of the table then the ‘3’ shall be encountered and the ECU will reset A Tooth to 0. The channels Sync Error and Timing Error will be incremented if this event occurs.

It is expected that the synchronization event(s) will be detected before the ‘3’ value is encountered, which would also result in A Tooth being reset to 0.

Active edges (internal teeth) are used to schedule fuelling and ignition events and are indicated by either ‘1’ or ‘5’ in the table. The ECU increments internal tooth counters Fuel Tooth No and Ign Tooth No when an active edge (internal tooth) is encountered in the Tooth Control table.

The Synchronization Test bit (100), when set, will cause the ECU to test for synchronization. This allows for some reduction of CPU load when running at higher RPMs by skipping synchronization checks on all tooth interrupts (events) (which would be occurring much more frequently). This bit is normally set in the tooth control values near the end of the table where the missing / extra tooth is approaching, though for some other patterns there could be multiple synchronization points.

When not synchronized (Stat Sync'd == OFF), the ECU can be configured to test for synchronization on all actual teeth by setting Test Not Sync'd to ON (recommended).

Tachometer Output

Overview

The ECU may be configured to output a tachometer signal to drive an external tachometer. The signal is a square wave with a frequency proportional to the engine speed.

Tacho Edge Table

Tachometer state change events are inserted into the Tacho Edge table. They should be evenly spaced and typically there should be 4 state changes per revolution (i.e. 2 pulses per rev), depending upon the tachometer input requirements.

It is generally best, therefore, to place the state changes at the same A Tooth numbers as equidistant ‘active edges’ in the tooth control table, assuming that it is possible to do so.

The Tacho Pin option specifies which ECU pin the tachometer signal is output from. Check the ECU pinout to determine which pin number this should be set to.

If using the RPM Pickup wizard, the Tachometer output can be calculated for you given a pulse-per-rev value. The RPM Pickup wizard assumes that Wheel Teeth is equal to the number of internal teeth.