small coprocessor

-------- REGISTERS --------
A - accumulator, 8-bit
X - index, 8-bit
Y - index, 8-bit
SP - stack pointer, 6-bit?
PC - program counter, 12-bit
F - flags: carry, negative, zero

3KB of RAM to put the program and data in

-------- OPCODE FORMAT --------
ffffff00                   - zero
ffffff01 nnnnnnnn          - zeropage (or immediate)
ffffff10 nnnnnnnn nnnnnnnn - absolute
ffffff11 nnnnnnnn nnnnnnnn - absolute,x

The bottom two bits tell the CPU how many bytes of parameters to read and put into a buffer.
For a constant it may be zero or an 8-bit value. Absolute and Absolute,x are reserved.
For memory it may be zero (first byte of RAM), zeropage, absolute or absolute,x.
For a branch, an 8-bit parameter is relative and a 16-bit parameter is absolute. Jumping to absolute,x is allowed.
Memory+Y acts like (zeropage),y for zeropage instructions.

f = function, from list below:

-------- FUNCTION TABLE --------
000000 00 LDA constant
000001 01 LDA memory
000010 02 LDX constant
000011 03 LDX memory
000100 04 LDY constant
000101 05 LDY memory
000110 06 CLC
000111 07 SEC
001000 08 ADD constant
001001 09 ADD memory
001010 0A SUB constant
001011 0B SUB memory
001100 0C ADC constant
001101 0D ADC memory
001110 0E SBC constant
001111 0F SBC memory
010000 10 NOR constant
010001 11 NOR memory
010010 12 XOR constant
010011 13 XOR memory
010100 14 CMP constant
010101 15 CMP memory
010110 16 CPX constant
010111 17 CPX memory
011000 18 ASL
011001 19 ROL memory
011010 1A LSR
011011 1B ROR memory
011100 1C CPY constant
011101 1D INC memory
011110 1E Unused
011111 1F DEC memory
100000 20 NOP            - neither TAX or TXA firing
100001 21 STA memory
100010 22 TAX
100011 23 STX memory
100100 24 TXA
100101 25 STY memory
100110 26 SWAP (X and Y) - TAX and TXA firing at the same time
100111 27 RTS
101000 28 LDA memory+y
101001 29 STA memory+y
101010 3A INC
101011 3B DEC
101100 3C INX
101101 3D DEX
101110 2E INY
101111 2F DEY
110000 30 PHP
110001 31 PLP
110010 32 PHA
110011 33 PLA
110100 34 PHX
110101 35 PLX
110110 36 PHY
110111 37 PLY
111000 38 BRA/JMP location
111001 39 BSR/JSR location
111010 3A BPL/JPL location
111011 3B BMI/JMI location
111100 3C BNE/JNE location
111101 3D BEQ/JEQ location
111110 3E BCC/JCC location
111111 3F BCS/JCS location