69 lines
1.8 KiB
Markdown
69 lines
1.8 KiB
Markdown
# Paper computer simulator experiment
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## TODO
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- [ ] Document current state of affairs (how to run it etc)
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Computer:
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- [ ] Implement carry flag on SUB
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Assembler:
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- [x] Allow comment-only lines
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- [x] Add labels
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Misc:
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- [ ] Write some more complex test programs
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- [ ] Consider adding a way to visualize screen memory
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- [ ] Do a proper binary version...
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## Instruction set
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0 END
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1 STO lit# ; store ... mem[lit#] <- A
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2 STO addr ; store ... mem[mem[addr]] <- A
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3 LDA lit# ; load ... A <- lit#
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4 LDA addr ; load ... A <- mem[addr]
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5 ADD lit# ; add ... A <- A + lit# ... and un/set carry flag
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6 ADD addr ; add ... A <- A + mem[addr] ... and un/set carry flag
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7 SUB lit# ; sub ... A <- A - lit# ... and un/set carry flag
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8 SUB addr ; sub ... A <- A - mem[addr] ... and un/set carry flag
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9 HOP lit# ; hop ... skip next instruction if A == lit# ... when true: IP <- PC + 2
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A HOP addr ; hop ... skip next instruction if A == addr ... when true: IP <- PC + 2
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B JMP lit# ; jump ... IP <- lit#
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C JMP addr ; jump ... IP <- addr
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D CCF ———— ; clear Carry Flag ... CF = 0
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E CHP ———— ; carry hop ... skip next instruction if Carry Flag is set ... when true: IP <- PC + 2
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F
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### Nice features that didn't fit
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- hop `IF<` and hop `IF>`
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- `MUL` and `DIV`
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- rotates and shifts
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## Registers
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- `A` - accumulator
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- `IP` - instruction pointer (aka program counter)
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## Flags
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- `CF` - carry flag
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## Memory-mapped peripherals
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- 4x4 display
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- hex keypad (details TBD)
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- ? bank selector (for bank-switching)
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### Maybe someday
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- timer (for a version in software/electronic-hardware)
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## Tentative memory map
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00-0F - display
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10-1F - keypad? (details TBD)
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20 - initial value for IP ?
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21-FF - free |