80s BMW On-Board Computer Hacking

The purpose of this project is to rebuild the internals of the BMW OBC found in the e24/28/30 cars. All the internals will be replaced except for the backlight, display, and keypad circuitry. To accomplish this I'll need to reverse engineer the display protocol and reverse engineer the keypad controls.

Display API

void set_ascii_digit

Params

• Digits digit to set, can be any of the 7-segment or 16-segment digits
• char val to set the digit to. All ASCII characters from 0x20 to 0xFF are accepted. Not all segments can render all digits so be sure to check the reference for 16-segment and 7-segment digits.
• bool decimal sets the decimal point on or off for digits 2 and 3. For digit 1 this flag will enable the H and I segments as part of the plus. The H and I segments can also be enabled by setting val to a "+" symbol.

void set_ascii_digit(enum Digits digit, char val, bool decimal);

void set_digit

The set_digit function will allow arbitrary setting of digit segments. This can be used to create output outside of the standard ASCII characters.

I could just give direct access to the digits array but I'm planning on reducing the ASCII map & bit shifting to just one ASCII map. In that case I may want to have this set function to sanitize the digit states. Sanitation could also be done while copying the digit states to the display buffer.

Params

• Digit digit to set
• short state of the digit

void set_digit(Digit digit, short state);

(Potential) void set_blink

The blink function will allow the dispay to blink (flash) at a specified interval.

Params

• bool enable the flash behavior
• short digits to flash, bit 0 = digit 1, bit 7 = digit 8, bit 8 = colon 1, bit 9 = colon2
• int period of time from turning the digits on, off, and on again.

void set_blink(bool enable = 1, short digits = 0x03FF, int period = 1000);

(Potential) void write_str

Writes a string across all digits of the display. Valid positions for the colon There should be a space between the 4th and 5th digit. The first group of digits will be right aligned on either the space between the 4th and 5th digits. If the + symbol is followed immediately by a non space character then the text will be left aligned to the +. Strings should be null terminated.

params

• char* str to write to the display
• return true if the string could be written, false if there were errors parsing the string

Examples

write_str("12:45 am\0");
write_str("12.:3.4 56:78\0");
write_str("12:34 56:78\0");
write_str("AB:CD EF:GH\0");
write_str("12.:34 56:78\0");
write_str("12.34 56:78\0");
write_str("12.3.4 5678\0");
write_str("1234 5678\0");
write_str("12.34 TEST\0");
write_str("12:34 TEST\0");
write_str("+ 12 TEST\0");
write_str("+12 TEST\0");
write_str("DISP TEST\0");

bool write_str(char* str);

Enum Digits

Used when accessing the digits state array.

enum Digits {
    DIGIT_1 = 1,
    DIGIT_2 = 2,
    DIGIT_3 = 3,
    DIGIT_4 = 4,
    DIGIT_5 = 5,
    DIGIT_6 = 6,
    DIGIT_7 = 7,
    DIGIT_8 = 8, 
    COLON_1 = 9,
    COLON_2 = 10
};