This is firmware for an MRS Microplex 7X installed in an M57-swapped BMW E36 M3. It implements the following functions:
- Brake, tail and rain light management.
- Fuel level sensing / reporting.
- DDE and EGS parameter reading and reformatting.
The vehicle electronic system consists of this module, the M57 DDE, ZF 6HP transmission controller (EGS), fuel pump controller (EKPM), MK60 ABS, and an AiM PDM08.
Brake lights are controlled directly by the CAN brake switch signal sent by the DDE.
Tail and rain lights are controlled by bits in a custom CAN stream sent by the PDM08.
The fuel level sensor in the fuel cell produces a 0.5-4.5V signal from empty to full; this is sampled by firmware, smoothed and the resulting value sent via CAN to the PDM08
Firmware uses the BMW parameter reading protocol to query DDE and EGS parameters, then reports these in a fashion that the PDM08 can handle.
The BMW parameter protocol is essentially their K-line protocol encapsulated in ISO-TP https://en.wikipedia.org/wiki/ISO_15765-2 frames with extended addressing. To keep things simple, we only query a single PID per message.
XXX is this correct? is there a more compact query format?
| CAN ID | Byte 0 | Byte 1 | Byte 2 | Byte 3 | Byte 4 | Byte 5 | Byte 6 | Byte 7 |
|---|---|---|---|---|---|---|---|---|
| 0x6f1 | ECU ID | length | 0x2c | 0x10 | PID0 | PID1 | 0x00 | 0x00 |
ECU ID : 0x12 = DDE, 0x18 = EGS length : 5..7 depending on the length of PID data PIDx : PID bytes (see below)
| CAN ID | Byte 0 | Byte 1 | Byte 2 | Byte 3 | Byte 4..7 |
|---|---|---|---|---|---|
| ECU ID | 0xf1 | length | 0x6c | 0x10 | Data 0..3 |
ECU ID : 0x612 = DDE, 0x618 = EGS length : 5..7 depending on the length of the data Data : parameter data, unused bytes are 0xff
| PID0 | PID1 | response | description |
|---|---|---|---|
| 0x03 | 0x85 | TH TL | fuel temperature in °C = (TH:TL / 100) - 55 |
| 0x04 | 0x1b | TH TL | exhaust temperature in °C = (TH:TL / 32) - 50 |
| 0x07 | 0x6f | TH TL | manifold air temperature in °C = (TH:TL / 100) - 100 |
| 0x07 | 0x6d | PH PL | PH:PL = manifold pressure in mBar |
| 0x0a | 0x8d | SS | oil pressure status, 00 = OK, 01 = low oil pressure |
| 0x0e | 0xa6 | GG | current gear = GG |
| 0x10 | 0x06 | SS | MIL indicator status |
| CAN ID | Byte 0 | Byte 1 | Byte 2 | Byte 3 | Byte 4 | Byte 5 | Byte 6 | Byte 7 |
|---|---|---|---|---|---|---|---|---|
| 0x6f1 | 0x18 | 0x02 | 0x21 | PID | 0x00 | 0x00 | 0x00 | 0x00 |
| CAN ID | Byte 0 | Byte 1 | Byte 2 | Byte 3 | Byte 4 | Byte 5 | Byte 6 | Byte 7 |
|---|---|---|---|---|---|---|---|---|
| 0x618 | 0xf1 | 0x03 | 0x61 | PID | 0x00 | 0x00 | 0x00 | 0x00 |
| PID | response | description |
|---|---|---|
| 0x01 | TT | EGS oil temperature (0x43 = ambient, perhaps °C - 50) XXX verify |
| 0x0a | GG | actual gear (GG = gear) |
| 0x0b | LL | EGS lockup (00 = not locked up) |
| 0x0c | VV | T30 voltage (0xae ~= 14v) XXX test |
| 0x18 | SS | selected gear (1 "P" 2 "R" 4 "N" 8 "D") XXX verify |
| 0x1a | LL | limp mode (89 = in limp mode) |