M221 Technical Specification
29T-068696TK-03

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 (pending).

The ECU V_GND (pin A31) and sensor ground (pins A40) are directly connected together via a ground plane in the ECU PCB. The ECU case is capacitively coupled to V_GND.

The ECU is designed for 12V or 24V vehicles, with various modes of operation based on the voltage (see Table 1.1, “Specification”). The ECU is protected against reverse supply connection. 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

In order to power the ECU from a sleep state, the power supply pin (V_PWR A2) must be powered and at least one of the following must occur:

The ECU will remain powered as long as the power supply pin (V_PWR A2) is connected to a power supply and any one of the following signals are asserted:

In order to shut the ECU down, the CAN transceiver on pins A28 and A43 must be placed into its shutdown state. To place the transceiver into its shutdown state, the DOT disable-CAN must be toggled at a frequency of 1 Hz and a duty cycle of 50%.

The application software must monitor the CAN bus and determine if it is appropriate to shut the ECU down by disabling the CAN transceiver.

The internal power hold signal 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 hold-PSU channel needs to be asserted. Setting this internal channel high will hold power when the key position input is opened, setting it low will allow the ECU to power off when the key position input is opened.

The ECU provides one external sensor power supply (pin A25). The sensor supply can be switched off using DOT enable-EXT-PSU1 to allow the application software to perform intrusive diagnostics on sensors.

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

The analogue inputs (pins A4, A5, A15, A18, A19, A20, A21 and A22) sample voltage with varying resolution and range. See the pin information for more details.

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,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 M221 family has provision for an internal temperature sensor measured by AIN internal-ecu-temp. This temperature sensor is unpopulated by default, so measurements of this signal will report 0 V.

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. The exact voltage being produced can be read on a scaled ADC channel, Vext_psu = (Vadc * 37.7)/33. 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 analogue input pin can be read on a direct (unscaled) ADC channel. Standard 0-5V inputs are passed directly to the ADC with no scaling.

Some analogue input pins are internally pulled up to the sensor power supply (pin A25). If the sensor supply is not enabled, floating inputs will fluctuate when read by the ADC. The sensor supply must be enabled for voltage measurements made on any of these channels.

The digital inputs (pins A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A26, A27, A29, A41, A42 and A44) sense the binary state based on the pin voltage and a threshold.

Pins A1, A17, A30 and A46 are configured as low-side — the ECU switches the output pin to ground, the load is connected to the output pin and the battery.

Figure 4.3. Low-side switching arrangement for digital outputs

These 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.

The voltage of the digital output pins A1, A17, A30 and A46 can be monitored using a corresponding internal Monitor (v) channel. The analogue monitor channel measures the actual voltage at the pin after scaling according to the equation

measured voltage (Vm, 0 to 5V) to actual voltage (Va, 0 to 36.9V): Va = Vm*347/47

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 digital outputs A1, A17, A30 and A46 are self protected by a thermal shutdown circuit. This protection is based only on output driver chip temperature and is independent of operating voltage.

Over-temperature shutoff occurs in the range 150 to 190 ºC (170 ºC typical). The device automatically restarts when temperature falls approximately 15 ºC below cutoff temperature.

An application can monitor these outputs for thermal shutdown via the Monitor (tt) analogue input channels for the corresponding outputs. See Table 4.5, “Low-side digital output thermal trip” for threshold values.

The injector outputs (pins A16, A32, A33, A34, A35, A36, A37, A38, A39 and A45) are peak and hold injectors controlled by the associated injector trigger inputs A6, A7, A8, A9, A10, A11, A12, A13, A14 and A15 and the injector clock controlled by PWM output DOT injector-clock.

The application must set the DOT injector-clock output to the desired dither frequency and 50% duty cycle for proper operation.

When a trigger input pin for an injector transitions from high to low, the associated injector output will be turned on. The output current will be allowed to rise to the peak current of 4A, then will immediately be limited to the hold current of 1A. See Figure 4.4, “Normal injector operation” for the normal operation waveform. See Table 4.6, “Injector current thresholds” for the range of peak and hold currents.

Figure 4.4. Normal injector operation

Figure 4.5. Injector operation under timeout

The injector trigger input must be high for at least (pending) ms to re-enable the peak current threshold after an output is switched off.

The injector outputs (A16, A32, A33, A34, A35, A36, A37, A38, A39 and A45) include output state and short-to-battery monitors.

The digital and analogue state monitors Monitor (d), Monitor (v), respectively, for the injector output pins reflect the state of the output pin. A short to ground or open-circuit condition is indicated if the Monitor (d) remains zero or the Monitor (v) remains below a threshold. See Table 4.7, “Injector Diagnostic Monitor(v) thresholds” for threshold levels.

The M221 injector output hardware monitors the outputs for short to battery operation. This detection requires an injector to be activated, and the hardware latches the first detected fault until the application reads the fault flag status. The faults are made available by reading the Monitor (sb) digital inputs (see Table 4.8, “Injector Diagnostic Monitor(sb) levels”). The platform will set the DIN injector-batt-fault digital input to 1 when a new injector short-to-battery fault has been detected.

An application should read the Monitor (sb) digital inputs at a fast rate to ensure that it detects all occurrences of faults on each injector. If a short-to-battery fault is detected on one injector, no other injectors can register a fault until that first fault is read by the application.

Reading the Monitor (sb) input for an injector will reset the fault flag for that output as well as the DIN injector-batt-fault fault flag.

The injector short to battery protection acts as a current limit; the output will still be active as long as the input trigger pin is low but the current will be limited to the hold current of 1A.

The M221 provides a variable resistance output on A3.

The resistance is controlled by using a SPI based digital potentiometer. The output of the digital potentiometer is controlled from software by commanding it to a percentage of its total range. The digital potentiometer resistance is calculated according to the following transfer function:

Digital potentiometer resistance = (50000 Ohm * commanded percentage) + wiper resistance

Where the wiper resistance is between 50 and 100 Ohm.

The overall circuit resistance is then calculated according to the following equation:

resistance = (50300 / (Digital potentiometer resistance)) * 3.9 Ohm + 3.9 Ohm.

The output is protected for over-current. If the current through the effective resistance exceeds approximately 1A, the hardware will assert the Monitor (ct) digital input and set the input to its maximum resistance.

If the current trip is asserted, the application should reduce the digital poteniometer resistance to its minimum (highest circuit resistance), then set the DOT fault-clear to one to re-enable the output.

The CAN busses (pins A23+A24 and A28+A43) are implemented using high-speed CAN transceivers. Neither CAN bus has terminating resistors.

CAN bus 0 (pins A28+A43) will wake the ECU from shutdown mode if traffic is detected on that bus.

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 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 voltage on the A27 pin.

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.