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Instruction set

A project log for 8-bit 74xx computer

Designing and building my own 8-bit computer from scratch with 74xx (TTL) logic chips

Ruud van FalierRuud van Falier 04/29/2018 at 11:371 Comment

I've done a bit more work on defining the instruction set.
These are the instructions that I'm planning to implement and that should be supported by the architecture that has been worked out so far:

MOV [A,B,X,Y] [A,B,X,Y] Copy register n1 to register n2
MVI [A,B,X,Y] #value Copy immediate value to register n
LD [A,B,X,Y] $address Load register n with value at memory address
ST [A,B,X,Y] $address Store register n value at memory address
ADD A + B → A
SUB A - B → A
AND A & B → A
OR A | B → A
XOR A ⊕ B → A
INC A + 1 → A
DEC A - 1 → A
RAL Rotate all bits in register A to the left
RAR Rotate all bits in register A to the right
JMP $address Jump to memory address
JZ $address Jump to memory address if zero flag is set
JNZ $address Jump to memory address if zero flag is not set
JC $address Jump to memory address if carry flag is set
JNC $address Jump to memory address if carry flag is not set
CALL $address Jump to subroutine at memory address
RET Return from subroutine
NOP Do nothing
HLT Halt execution
IN Load data from input into register A (needs to be worked out)
OUT Output data from register A (needs to be worked out)

I haven't given much thought to input & output yet, so I might need a few specialized instructions in the future to cover that part.

Discussions

hosabike wrote 05/04/2018 at 19:47 point

Is this RISC architecture?

  Are you sure? yes | no