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Currently the main site is Dippy.

Instruction set

If top bit set, then JSR to remaining 9 bit address.

If next bit set, load immediate the lower 8 bits (possibly sign extended)

Everything else is 3 bit conditional (1, lt0, le0, eq0, ne0, ge0, gt0, 0)

If top bit set, then JMP the remaining 4 bits (-8 to +7)

else have a 4 bit instruction space (IN, OUT, RET, D2R/R2D/R, DROP,SWAP, NOT, INC/DEC, AND/OR/XOR/ADD/SUB/ADDc/SUBc - yes that's already 18).


At about 3cm2 for a DIP switch (8 or 10 bit plus a LED to show that switch is active) then

  • 8 bit address space, 256 words, 0.75m2, will fit on A0 (1m2)
  • 9 bit address space, 512 words, 1.5m2, won't fit in A0 but cost < £100
  • 10 bit address space, 1024 words, 3m2, may not even fit in a car and cost > £100

That's a pain as 8 bits not enough for instruction set any more.

Maybe 10 bit data, 9 bit address space?


dippy_computer.txt · Last modified: 2019/02/20 09:27 by admin