Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

Hi Doddy,

Yeh an FPGA would be an excellent choice although I don't have any non-BGA parts here and didn't want send out for 4 layer board to be made. Lattice have some TQFP parts that could be used but I haven't got any. I have some 485 line drivers though left over from running DMX lighting throughout my house, thanks for reminding me!

On the noise issue, it is being caused by the 328p sampling the differential pair wrt ground without removing the common mode noise (which will always be there). If I'm right it would be completely eliminated by properly terminating the pair with a line receiver.

The LUT does work nicely, I use an 8 bit address space at the moment, 6 input bits and 2 bits of state. I moved all my code into a loop that executes at startup, this iterates through the address space and writes the 8 bit output [2 bits of updated state as the FSM transitions, 6 bits of compressed output] into a 256byte block of memory aligned on 256byte memory boundaries. This removes the need to hand craft a LUT, all you are really doing is executing your logic for every possible input and caching the result.

Then the actual runtime programme loop written in assembler reads the input port directly into the lower byte of the indirect addressing register pair, debounces, merges in the 2 bits of state, immediately does the lookup, this is made very easy by keeping the LUT is aligned with a 256 byte memory boundary.

The assembler the decompresses the output bits, writes them out and updates the state bits. Repeat ad-nauseum.