officialpixelbrush / pbpu2

PBPU2

A 4-Bit Fantasy CPU with basic I/O.

Registers

Letter	Name	Size
A	Accumulator	4-Bit
B	B-Register	4-Bit

A and B can be used together for Input/Output

Flags

Letter	Name
C	Carry
Z	Zero

Instructions

Num	Mnemonic	Description	Size
0	NOP	No Operation	1
1	LDAN num	Load Number into A	2
2	LDAM (mem)	Load Contents of Memory into A	4
3	STA (mem)	Load Contents of A into Memory	4
4	SWAP	Swap the Contents of A and B	1
5	SHFT	Shift A Left, Shifts Leftmost Bit into Carry	1
6	ADD	Add A with B, load result into A, Carry exists	1
7	SUB	Subtract B from A, Result in A, Borrow doesn't exist	1
8	AND	AND A with B, Result in A	1
9	OR	OR A with B, Result in A	1
A	XOR	XOR A with B, Result in A	1
B	IN	Wait for Input until Interrupt, load IO-Bus into AB (Can be used as HALT)	1
C	OUT	Output AB onto IO-Bus until Acknowledged	1
D	JP mem	Unconditional Jump	4
E	JPC mem	Conditional Jump, if Carry = 1, jump	4
F	JPZ mem	Conditional Jump, if Zero = 1, jump	4

Memory

2^(3x4), aka 2^12 4096x4 Address Space