8-Bit Emulator

Instructions

Registers are written as Rx in the assembly, where x is a register from 0-15. In the machine code a register is 4 bits and a number or address is 1 byte.

Hex Opcode	Assembly	Memory Layout (hex)	Description
0x00	NOP	00	Null operator
0x10	LOAD [reg] [addr]	1x xx	Load byte from memory location addr into register reg
0x20	STORE [reg] [addr]	2x xx	Store byte from register reg into memory location addr
0x30	BRANCH [label]	30 xx	Set PC to address of label
0x40	SET [reg] [byte]	4x xx	Store byte in register reg
0x50	ADD [reg] [byte]	5x xx	Add byte to register reg
0x60	SUB [reg] [byte]	6x xx	Subtract byte from register reg
0x70	BNZ [reg] [label]	7x xx	Set PC to address of label if reg is not zero
0x80	EXIT	80	Stop processing

Assembly Directives

Directive	Assembles to (hex)	Description
DEF [byte]	xx	Store byte into current memory location

Example Assembly

NOP
bob:
SET     r4   10
loop:   ;this is a label
SUB     r4   1
ADD     r2   1
BNZ     r4   loop
EXIT
BRANCH  bob