8-bit Computer

Instruction Set

This table shows every instruction available to programs on the computer, as well as a small description of their functionalities. An "x" in third column indicates that the instruction uses an argument.

RAM[x] denotes the value at memory location x. A and B correspond to the values of the A and B registers, and ACC stands for the accumulator register.

0	0000 0000	HALT		Stop the program from running.
	0000 0001	LDA	x	Load RAM[x] into ACC.
	0000 0010	STA	x	Store ACC in RAM[x].
	0000 0011	OUT		Show ACC on the output display.
4	0000 0100	NO-OP		Do absolutely nothing.
	0000 0101	MEMREFLD	x	Load RAM[RAM[x]] into ACC.
	0000 0110	A->B		Copy the value of A to B.
	0000 0111	A->ACC		Copy the value of A to ACC.
8	0000 1000	AREFLD		Load RAM[A] into ACC.
	0000 1001	B->A		Copy the value of B to A.
	0000 1010	BREFLD		Load RAM[B] into ACC.
	0000 1011	B->ACC		Copy the value of B to ACC.
12	0000 1100	MEMREFST	x	Store ACC in RAM[RAM[x]].
	0000 1101	ACC->A		Copy the value of ACC to A.
	0000 1110	ACC->B		Copy the value of ACC to B.
	0000 1111	AREFST		Store ACC in RAM[A].
16	0001 0000	ADDR	x	Add RAM[x] to ACC.
	0001 0001	ADDA		Add A to ACC.
	0001 0010	ADDB		Add B to ACC.
	0001 0011	BREFST		Store ACC in RAM[B].
20	0001 0100	SUBR	x	Subtract RAM[x] from ACC.
	0001 0101	SUBA		Subtract A from ACC.
	0001 0110	SUBB		Subtract B from ACC.
	0001 0111	PAGE	x	Switch the active page to x.
24	0001 1000	JMP	x	Jump to address x.
	0001 1001	JZ	x	Jump to address x if ZERO is set.
	0001 1010	JC	x	Jump to address x if CARRY is set.
	0001 1011	PUSH		Push ACC to the top of the stack.
28	0001 1100	POP		Pop the top of the stack into ACC.
	0001 1101	CALL x		Call the function at address x.
	0001 1110	RETURN		Return from the current function.

Assembly and Machine Code

Programs are either written in assembly language or machine code. The machine code, when placed in RAM, begins execution at memory address 0. Then, every instruction takes up two bytes: one for the opcode and one for the argument. If no argument is required for a particular instruction, anything can be used, but 0 is common.

Assembly also uses a very simple format. A typical assembly program might look like this:

	LDA	50	Push two numbers, 1 and 2, to the stack.
	PUSH
	LDA	51
	PUSH
	LDA	52	Clear the accumulator.
	POP	0	Then, pop and output the two numbers.
	OUT	0	They should be displayed in reverse order.
	POP
	OUT
	HALT
	
50	DATA	1
51	DATA	2
52	DATA	0

The first column is the address of the instruction or data. The second column is the mnemonic of the instruction to execute. The third column is the argument to that instruction. And, any text after the third column is considered a comment and ignored. Additionally, the first and third