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Car.cpp
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EngineData.cpp
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EngineData.h
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IC_CUSTOM_TEXT.ino
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README.md
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can.h
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README.md

Custom instrument cluster text

Findings on how the W203's IC works

The IC will expect 1 or both of the following packet sequences to ID 0x1A4

  1. Header text -> 2 8bit packets
  2. Body text -> 3 8bit packets

Displaying header text

Limitations

Must be 3 ASCII characters. If less, pad it out with spaces!

Displaying body text

Limitations

Must be at MOST 9 characters, and no less than 5. Any more won't get displayed by default, and any less MUST be padded with spaces.

Can frame structure

ID DLC Byte 1 Byte 2 Byte 3 Byte 4 Byte 5 byte 6 Byte 7 Byte 8
0x01A4 8 0x10 CSA 0x03 0x26 0x01 0x00 0x01 CSB
0x01A4 8 0x21 0x10 A0 A1 A2 A3 A4 A5
0x01A4 8 0x22 A6 A7 A8 A9 A10 0x20 0x00

CSA -> Check Sum A CSB -> Check Sum B A0-9 -> Body data bytes

Check sum A/B

Check Sum B is the number of ASCII Characters to display minus plus 2
Check Sum A is calculated using 7+CSB

A0-10

This is character count dependent, but will follow the same structure for n characters, where n <= 9:
A0-An-1 -> ASCII values of characters to display
An -> 0x00 An+1 -> Check Sum C

Any remaining bytes are left as 0x00, for example for 5 character strings, the last 4 bytes are left as 0x00

Check Sum C

** By far the HARDEST one to work out! This was the magic token **

The IC appears to use the following table for calculating what the checksum should be:

Num. of chars Value 1 Value 2 Value 3 Value 4
9 ASCII chars 1073 817 561 305
8 ASCII chars 1090 834 578 322
7 ASCII chars 1136 880 624 368
6 ASCII chars 1121 865 609 353
5 ASCII chars 1135 879 623 367

The IC Expects Check sum C to be calculated using the following algorithm:

  1. Sum All the ASCII characters in text
  2. Find the first value in the row for n number of ASCII characters, where it minus the Sum Calculated in Step 1 is less than 256. Call this the look up value
  3. Check Sum C = Look up value - Sum of ASCII characters.

Example

Text -> "Testing!"
Number of chars -> 8

First packet
CSB = 9+2 = 11 (0x0B)
CSA = 11+7 = 12 (0x12)

Second packet A0 = T (0x54)
A1 = e (0x65)
A2 = s (0x73)
A3 = t (0x74)
A4 = i (0x69)
A5 = n (0x6e)

Third packet
A6 = g (0x67)
A7 = ! (0x21)
A8 = 00 (0x00)
A9 = 834-767 = 67 (0x43)
A10 = 00 (0x00)