Makin' a home-brewn dashboard program, and I need theory help!

[Dave Flowerday]

There's all kinds of tricks you can pull to cram more data through those 8 bits. If you need to send back two values, you can use one of those bits to indicate which value you are sending, then use the other 7 bits as the value. For instance, use the most significant bit as the value selector:

Bits
7 6 5 4 3 2 1 0
----------------------
0 0 0 0 0 0 0 1 = Variable A = 1
1 0 0 0 0 0 0 1 = Variable B = 1

This way you can send back a number between 0 and 127 for each variable and just alternate which one you send. You can carry this idea further and trade a bit of precision for another power of 2 of variables, i.e. 6 bits for the value, 2 bits for the variable number, etc.

If you need to send back lots of values and only need to do so a couple times a second, you could something like this: Send the values 0xFF, 0x01, 0xFE, 0x26, 0xFF, 0x02, 0xFE, 0x67... In this sequence, 0xFF is an attention signal: it means that the next number will be the variable number. Then 0xFE is another attention signal and means that the following number is the variable data. So the above sequence tells you that variable 1 == 0x26 and variable 2 == 0x67. Now obviously you can't use 0xFF and 0XFE as either a variable number of a variable value. The downside to this is that it takes 4 dashboard packets to send each value, so you can only send 10 variables a second. There's also a problem which is that you don't know exactly when the master CPU is going to send a packet, so you can't really send 40 different bytes a second. Probably it's more like 10-15 bytes a second, so using this method you could maybe send like 2 to 4 variables per second.

Anyway, I hope this gives you some ideas. Basically you can do a lot with 8 bits by trading either time or precision. Sorry for rambling on so long