M250 Technical Specification
29T-068276TK-05

This technical specification relates to the following ECU variant:

Various input and output functionality is supported where some pins may be capable of more than one function. Some functions require a combination of pins but not all pin combinations are possible.

Connector packs can be ordered from Pi. Individual connector components can be ordered from Pi or from various manufacturers.

The power supply pin (V_PWR A2) and the ground pin (V_GND A31) are both rated to 40A.

The ECU is designed for 12V or 24V vehicles and will operate over the range 6.5V to 36V. The ECU is protected against reverse supply connection (for at least 60 seconds). All inputs and outputs are protected against short-to-V_PWR or short-to-V_GND over normal operating range.

The ECU power arrangement is shown in Figure 4.1, “Switching arrangement for main power supply”.

Figure 4.1. Switching arrangement for main power supply

The ECU is powered up when the power supply pins (V_PWR A2) and key position (ignition sense) input (pin A26) are asserted. The key position input (pin A26) can be read as a digital input.

This arrangement allows for the ECU application software to hold the ECU on after the external key position input is opened, allowing, for example, non-volatile memory processing to occur. For the ECU to hold power the internal DOT disable-PSU-hold channel needs to be asserted. Setting this internal channel low will hold power when the key position input is opened, setting it high will allow the ECU to power off when the key position input is opened.

The ECU can provide power to actuators through a high-side power pin (A16) and control if this pin is asserted or not. See Section 4.13, “Digital output — high-side actuator output control” for further details.

The ECU provides two external sensor power supplies (pins A25 and A39). Each sensor supply can be switched off by setting the appropriate internal channel (DOT disable-EXT-PSU1 or DOT disable-EXT-PSU2) to one, to allow the application software to perform intrusive diagnostics on sensors.

Each output is monitored by an internal analogue input channel which can be used to check for short circuits and measure the exact output voltage for use with ratiometric sensors.

The output voltage is guaranteed to never reach full scale in normal operation, hence a full scale indication should be taken to indicate a suspected short to battery. The value read from the voltage monitor when the corresponding PSU is enabled should be interpreted as follows:

The value read from the common sensor ground voltage monitor should be interpreted as follows:

The sensor ground feedback can also be used in normal operation by the application software to provide a precision ground reference for ratiometric measurements.

The analogue inputs (pins A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A19, A20, A21, A22, A23 and A24) sample voltage with varying resolution and range. See the pin information for more details. Some of the analogue inputs have additional characteristics, as detailed in the following sections.

Ratiometric sensors are read in as a ratio between the sensor and reference voltages (V_sens/V_ref). Correction is only required on channels for which an absolute voltage measurement is required. Correction is not required for sensors supplied from the 5V sensor supply and which produce an output that is ratiometric to the supply.

To read a variable sensor which is an absolute referenced sensor (V_sens,V_abs) the V_ref for the ADC requires correction:

Where V_MEASURED is the A/D conversion for an external pin, V_REF is the A/D conversion for internal channel AIN VRH, V_2.5 is the A/D conversion for internal channel AIN PSU+2.5VD, and 2 is a constant.

The ECU has an internal temperature sensor. The relationship between temperature and the ADC voltage (V_ADC) for the internal temperature sensor is non-linear. The temperature over a range of -55°C to +150°C correlates to voltage by Table 4.3, “Internal temperature input”.

The ECU power arrangement is shown in Figure 4.2, “VREF arrangement”. The figure shows the relationship between the internal 5V V_REF and ground, the external sensor supply and ground, and the analogue inputs.

Figure 4.2. V_REF arrangement

The internal low precision 5V reference supplies the reference pin on the ADC. A high precision 2.5V reference can be read on a direct (unscaled) ADC channel. This can be used to calculate the true value of the 5V reference and subsequently used to improve accuracy on all other channels. The 5V reference is divided down to 4.95V to provide the external sensor supply. The exact voltage being produced can be read on a direct (unscaled) ADC channel. The sensor ground is a nominal 0V, but may be slightly above this due to voltage drop across the protection device.

The exact voltage on the pin can be read on a direct (unscaled) ADC channel. Standard 0-5V inputs are passed directly to the ADC with no scaling. RTD analogue inputs have a 10K pullup to the internal reference voltage. The voltage difference between the input and sensor ground is amplified by a gain of 12 and then passed to an ADC input.

The digital inputs (pins A10, A11, A12, A13, A14 and A15) sense the binary state based on the pin voltage and a threshold.

The digital outputs (pins A1, A17, A18, A30, A32, A33, A34, A35, A36, A45 and A46) can be used as low-side drivers. That is, the ECU switches the output pin to ground, the actuator is connected to the output pin and the battery (or to the ECU's high-side power pin, A16, see Section 4.13, “Digital output — high-side actuator output control” for further details).

Figure 4.3. Low-side switching arrangement for digital outputs

The low-side digital outputs contain internal monitoring circuitry that provides diagnostic information. However, as a consequence a small leakage current will flow through the actuator when the low-side output driver is turned off. Refer to Table 4.4, “Low-side digital output leakage current” for typical leakage currents at specified operating voltages.

When a pin is configured as a high-side, the ECU switches the output pin to V_PWR and the actuator is connected to the output pin and ground.

Figure 4.4. High-side switching arrangement for digital outputs

The actual state of an output pin can be monitored using a corresponding internal digital monitor and two internal analogue monitor channels. The digital monitor channel simply reflects the on or off state of the actual output. The analogue monitor channels measure the actual voltage and current at the pin after scaling.

When the pin is used as a PWM, there are two possible uses for such a feedback:

When the pin is used as a plain digital output, feedback is used as follows:

The over-current trip state of an output pin can be monitored using a corresponding internal over-current monitor channel. In normal operation the internal over-current trip channel will be one. If the output channel experiences an over-current, the output channel will be forced off by the ECU and the over-current trip channel will be set to zero.

The over-current trip latch can be cleared and the tripped outputs enabled by the pss_OvercurTripReset Simulink block or by calling the pss_overcur_trip_reset() C-API function.

The high-side output arrangement provides for a single switch (pin A16) to turn on or off actuators controlled by the ECU. Thus a load supplied by the high-side drive and controlled by a low-side drive has two independent means of being switched off, which is desirable for critical loads that must be turned off even if the low-side drive should fail in a conducting state.

Figure 4.5. Switched output control for digital outputs

The high-side actuator output (pin A16) has a number of internal monitor signals (digital, voltage and current trip). However, there is a connection between the low-side output pins and the high-side actuator output monitor signals which can result in incorrect monitor signals when the high-side output is unconnected.

Figure 4.6. High-side actuator output diagnostic

The diagram shows the connection between the low-side and high-side actuator outputs. The diode provides a current recirculation path for inductive loads. However, if both the low and high-side control is turned off, then the monitor signal should be ignored (especially if the low-side load has low resistance).

Recirculation diodes are present on output pins A18, A32, A33, A34, A35 and A45, however the diodes on A32, A33 and A34 are switched out of circuit when injector mode is selected and the output is switched off.

The injector outputs (pins A32, A33 and A34) allow the injector current to be regulated at two different levels, called the peak and the hold currents. The application software must provide two digital signals, one for the duration of the peak current and one for the duration of the peak and hold current. The application software must provide a clock for the injector current modulation (see internal channels A32, A33 and A34).

Figure 4.7. Injector operation

The internal injector clock channel must be configured to output a continuous 50% duty cycle square wave at an application determined frequency. This will typically be in the range 100Hz to 10KHz.

The peak and hold digital signals can be generated through the use of the pdx_PWMSynchronisedOutput Simulink block or the pdx_spwm_output() C-API function. The master channel corresponds to the peak signal, and the slave channel corresponds to the peak and hold signal. The master and slave channels must have identical frequency and the slave delay must be set to zero. The injector clock signal can be generated through the use of the pdx_PWMOutput or pdx_PWMVariableFrequencyOutput Simulink blocks or the pdx_pwm_output() C-API function.

The injector outputs (pins A32, A33 and A34) can be configured as either an injector output or a PWM output. The pin output mode can be selected through the use of the pcfg_Config_M250 Simulink block or the pcfg_setup_m250() C-API function.

When A32, A33 and A34 is configured as an injector channel, the corresponding internal current trip monitor channel will give undefined results.

The H-bridge outputs (pins ) are controlled through the pdx_HBridge_Output Simulink block or the pdx_hbridge_output() C-API function.

Figure 4.8. H-bridge arrangement

The H-Bridge can be driven in four modes:

The frequency and the duty cycle of operation are controlled by the application. There are monitor inputs to check the output pin state.

Some of the internal and external inputs and outputs are classed as serial. The connector pinout tables and internal channel tables above specify whether a pin or channel is serial or not.

When a serial input is read, the measurement reflects the value of the input taken last time the application task ended. I.e., the value of the input is delayed by one cycle of the task period. When a serial output is set, the driven state is updated at the end of the current application task. I.e., there is a delay between requesting a change in the output state, and the output state honoring that request.

The CAN buses (pins A28+A43 and A29+A44) are implemented using high-speed CAN transceivers. CAN bus 1 has terminating resistors fitted, CAN bus 0 doesn't.

The ECU supports different memory configurations for application, calibration and RAM sizes, some of which require external calibration RAM (see Section 4.22, “Memory — calibration capabilities”).

The ECU supports non-volatile memory storage in Flash. Battery backed RAM is not supported.

The processor's Flash memory is split into small and large memory blocks. The application and calibration are stored in large blocks, whilst DTC information, freeze frames and so on are stored in small blocks.

The largest Flash block can take up to approximately 7.5 seconds to erase. This occurs in an environment where the Flash has been erased and programmed many times at its temperature extreme. The typical erase time is smaller, especially at ambient temperatures. Reprogramming an ECU (where many large blocks would be erased), or storing DTC information across power cycles, can therefore take some time. Users and applications should take this into consideration.

The minimum number of erase cycles is approximately 1,000 for large Flash blocks and 100,000 for small Flash blocks. This occurs in an environment where the Flash has been erased and programmed many times at its temperature extreme. The typical number of erase cycles is larger, especially at ambient temperatures.

The minimum data retention is approximately 5 years for blocks which have been erased less than 100,000 times, and approximately 20 years for blocks which have been erased less than 1,000 times.

The information about the Flash has been taken from Freescale's MPC5534 Microcontroller Data Sheet document, revision 4 (dated Mar 2008).

The ECU supports both offline calibration (where all of the ECU's calibration memory is reprogrammed whilst the application is stopped) and online calibration (where individual calibrations can be modified whilst the application runs). These calibration capabilities are supported through two ECU types:

The ECU can run in one of two system modes: reprogramming mode and application mode. In reprogramming mode, the ECU can be reprogrammed with application software from a calibration tool. In application mode, the ECU runs the programmed application software. The ECU selects which mode to enter when it is powered up by measuring the external FEPS A27 pin.

The ECU also uses the FEPS input (pin A27) as an output to flash an optional LED. The LED is connected between V_PWR (pin A2) and FEPS (pin A27). Note that the pin use as FEPS input or as lamp output is mutually exclusive.

The flash sequence represents a set of codes. Each code is a three digit number, where each digit is flashed a number of times equal to its value.

An example would be the flash sequence for code 113. The flash sequence is broken down into a series on marks, or on and off pulses as follows:

Figure 4.9. Flash code sequence

Each of the marks lasts for a specific duration:

After the end code mark, the ECU will either flash the next code, or return to the start of the list and flash the first code. The ECU always has at least one code to flash.

Each code represents information about the ECU state. If there is no flash sequence, or a malformed flash sequence, then the ECU is malfunctioning. Otherwise, the flash sequence will represent one of the following codes:

Developer units have the capability to accept calibration changes while the application software is running.

The ECU closely adheres to the IEEE-754 for floating point numbers.

When using Simulink, floating point Simulink models are supported — all calculations are performed using single-precision (even if the model uses double-precision, the ECU performs calculations using single-precision).

When using the C-API, floating point applications are supported — all calculations are performed using single or double precision, as determined by the application code (although double precision will incur some software overhead — see the compiler reference manual for further details).

The rounding mode is set to round-to-nearest. In some conditions, the ECU will not adhere to the IEEE-754 standard:

The ECU does not generate ±Inf, NaN or a denormalised number as the result of a calculation.