cardiograph-computer/readme.md

Paper computer simulator experiment

TODO

• Implement CCF and CHP
• Implement carry flag on SUB
• Write some more complex test programs
• Consider adding a way to visualize screen memory
• Do a proper binary version...

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 D CCF ———— ; Clear Carry Flag ... CF = 0 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