The E30 instrument cluster for newer models have a coding plug (codier stecker) in front that stores the configuration parameters for SI boards: 6 or 4 cylinders, the maximum RPM, etc.
If you open the coding plug, you can find the chip HML087. It’s a 40-year-old ROM that uses its own communication protocol.
The coding plug pins
| Pin | Function | Description |
|---|---|---|
| 1 | CLOCK | The data is sent on its level going from high to low |
| 2 | GND | Ground |
| 3 | +5V | Power to the chip |
| 4 | GND | Ground |
| 5 | DATA | The output data: high – 1, low – 0 |
| 6 | GND | Ground |
| 7 | CS | The ROM is selected when the CS level is high |
| 8 | GND | Ground |
Communication protocol capture
The coding plug for HML087 1385468 (E30 325i M20B25 7000RPM USA)
The communication protocol description.
The pin CS is set high by a microprocessor. Then, the microprocessor sends 64 CLOCK signals. When the CLOCK signal goes from high to low, the ROM outputs data on the DATA pin.
Data from different E30 coding plugs
| Coding plug | Description | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1385468 | E30 325i M20B25 7000RPM USA | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 0 | 0 | 0 |
| 1380873 | E30 M3 S14 8000RPM Europe | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| 1377368 | E30 325e M20B27 5000RPM USA | 0 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | 1 |
| 1394321 | E30 318is M42B18 7000RPM USA | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 0 | 0 | 0 |
| 1385364 | E30 318i M40B18 7000RPM Europe | 1 | 0 | 1 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 0 | 0 | 0 |
| 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | ||
| 1385468 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 1380873 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 1377368 | 0 | 1 | 0 | 0 | 1 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | |
| 1394321 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 1385364 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | ||
| 1385468 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 1 | 0 | |
| 1380873 | 0 | 0 | 0 | 0 | 0 | 1 | 0 | 1 | 0 | 1 | 1 | 0 | 1 | 0 | 0 | 0 | |
| 1377368 | 0 | 1 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | |
| 1394321 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 1 | |
| 1385364 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 48 | 49 | 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 | 63 | ||
| 1385468 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 0 | |
| 1380873 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 1 | 0 | 1 | 1 | 1 | 1 | 0 | |
| 1377368 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | |
| 1394321 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | 1 | 1 | 1 | 0 | 1 | 1 | |
| 1385364 | 0 | 1 | 0 | 1 | 1 | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 1 | 0 | 0 | 0 |
HML087 emulation
The communication protocol can be emulated by a microprocessor. While the Attiny family looks like an obvious choice, it’s too slow for the application. It will work with older SI boards where the CLOCK signal duration is 30 µseconds, but in the newer SI boards the duration is 5 µseconds.
HML087 emulator that uses the microprocessor ch32v003
Here is the software for the BMW E30 coding plug emulator that uses the RISC-V microcontroller CH32V003: https://github.com/faritka/hml087