32-bit instructions. 4 bytes.
- Byte 0: opcode
- Byte 1: higher 4 bits for subfunction; lower 4 bits for Rz
- Byte 2:
- (R-type) higher 4 bits for Rx; lower 4 bits for Ry
- (I-type) all 8 bits for the upper 8 bits of the immediate value
- Byte 3:
- (R-type) not used
- (I-type) all 8 bits for the lower 8 bits of the immediate value
General format: ooooiitt
- Lower 2 bits
ttfor operations:- tt = 00: R-type instruction
- ooooii = 000000: (nop)
- ooooii = 000001: (add) Rz <- Rx + Ry
- ooooii = 000010: (sub) Rz <- Rx - Ry
- ooooii = 000011: (mul) Rz <- Rx * Ry
- ooooii = 000100: (div) Rz <- Rx / Ry
- ooooii = 001000: (load) Rz <- M[Rx + Ry]
- ooooii = 001001: (store) M[Rx + Ry] <- Rz
- tt = 01: I-type instruction
- ii = 00: Imm as unsigned memory address
- oooo = 0010: (jz) go to (PC+Imm) if Rz = 0
- oooo = 0011: (jp) go to (PC+Imm) if Rz > 0
- ii = 01: Imm as signed integer
- oooo = 0000: (li) load Rz with (extended) Imm
- ii = 00: Imm as unsigned memory address
- tt = 00: R-type instruction