1.3 KiB
Paper computer simulator experiment
ISA
0 END 1 STO lit# ; store ... mem[lit#] <- A 2 STO addr ; store ... mem[mem[addr]] <- A 3 LDA lit# ; load ... A <- lit# 4 LDA addr ; load ... A <- mem[addr] 5 ADD lit# ; add ... A <- A + lit# ... and un/set carry flag 6 ADD addr ; add ... A <- A + mem[addr] ... and un/set carry flag 7 SUB lit# ; sub ... A <- A - lit# ... and un/set carry flag 8 SUB addr ; sub ... A <- A - mem[addr] ... and un/set carry flag 9 HOP lit# ; skip next instruction if A == lit# ... when true: IP <- PC + 2 A HOP addr ; skip next instruction if A == addr ... when true: IP <- PC + 2 B JMP lit# ; ... IP <- lit# C JMP addr ; ... IP <- addr D CAT ---- ; Carry Flag Toggle ... CF <- !CF E CHP ---- ; skip next instruction if Carry Flag is set ... when true: IP <- PC + 2 F
Nice features that didn't fit
- hop IF< and hop IF>
- MUL and DIV
- rotates and shifts
Registers
- A -- accumulator
- IP -- instruction pointer (aka program counter)
Flags
- CF -- carry flag
Memory-mapped peripherals
- 4x4 display
- hex keypad (details TBD)
- ? bank selector (for bank-switching)
Maybe someday
- timer (for a version in software/electronic-hardware)
Tentative memory map
00-0F - display 10-1F - keypad? (details TBD) 20 - initial value for IP ? 21-FF - free