Specifications

Instruction Parameter Types

Parameter Type	Description
imm8	An immediate value (a constant value baked into the code at compile time). Usually present in the byte after the opcode
mem8	A type of immediate value used as a memory address in the lda and sto instructions with no structural difference
reg8	A register number, usually added to the base opcode value to differentiate between similar instructions with use or store values to different registers. The register numbers for the 4 general purpose registers are given below.

Instructions

Byte 0 (Opcode)	Byte 1	Instruction	Description
00-03	00-FF	sto <mem8>, <reg8>	Stores data in register to memory location
04-07	00-FF	lda <reg8>, <mem8>	Loads data into register from memory location
08-0B		jmprel <reg8>	Jumps a certain number of bytes ahead from the start of this instruction
0C	00-FF	jmprel <imm8>	Jumps a certain number of bytes ahead from the start of this instruction
0D	00-FF	sub <imm8>	Subtracts a value from register A
0E	00-FF	mul <imm8>	Multiplies register A by a value
0F	00-FF	add <imm8>	Adds a value to register A
10-13		mul <reg8>	Multiplies register A by a value
14-17		add <reg8>	Adds a value to register A
18-1B		sub <reg8>	Subtracts a value from register A
2C-2F		imul <reg8>	Signed multiplies register A by a value
30-33		iadd <reg8>	Signed adds register A by a value
34-37		neg <reg8>	Negates a value and stores in A
38	00-FF	imul <imm8>	Signed multiplies register A by a value
39	00-FF	iadd <imm8>	Signed adds register A by a value
3B	00-FF	jmpfar <imm8>	Jumps to an absolute address
3C-3F		cmp <reg8>	Compares register A to value and stores in flags
40	00-FF	cmp <imm8>	Compares register A to value and stores in flags
41	00-FF	or <imm8>	ORs register B with value and stores in register B
42		nop	No Operation
43	00-FF	and <imm8>	ANDs register B with value and stores in register B
44+bitmap	00-FF	jmprel <imm8>	Jumps a certain number of bytes ahead if bmap AND flags != 0 (bitmap in instruction itself and imm8 in byte after opcode).
4C-4F	00-07	jmprel <reg8>	Jumps a certain number of bytes ahead if bmap AND flags != 0 (reg8 in instruction itself and bitmap in byte after opcode).
50-53	00-FF	or <reg8>	ORs register B with value and stores in register B
54-57	00-FF	and <reg8>	ANDs register B with value and stores in register B
58	00-0F	mov <reg8>, <reg8>	Moves value from first reg8 into second reg8. (higher 2 bits are register A and lower 2 bits are register B)
59		out	Outputs data into port in register A with value in register B
5A		in	Inputs data from port in register A into register B
5B	00-01	features <imm8>	Returns the feature byte at a certain byte no. (given below) into register C
5C-5F	00-FF	mov <reg8>, <imm8>	Moves value into given register
60-63		features <reg8>	Returns the feature byte at a certain byte no. (given below) into register C
64		clf	Clears the flags register
65		nf	Negates the flags register
66		gf	Stores the flags register in register D
68-7B		not <reg8>	Bitwise NOT's a value and stores in B

Flags

Bit No	Name	Description
0	Equal	The values are equal
1	Less	Value A < Value B
2	Greater	Values B < Value A

Registers:

Register No	Name	Description
0	A	general purpose register used in math operations
1	B	general purpose register used in bitwise operations
2	C	general purpose register used for features operation
3	D	general purpose register used to interface with the flags register
4	PC	program counter, edited using jmp* instructions
5	FLAGS	flags register, edited using cmp instructions

List of Feature Attributes:

Byte 0:

8 bit CPU version (currently v0)

Byte 1:

Bit No	Description
0	16-bit supported
1	32-bit supported
2	64-bit supported
3-7	Unused

Architectural Limits

• 8 bit wide address lane
• Maximum memory size of 256 (can be circumvented by interfacing with an external memory module)
• 256 IO ports
• Currently 4 general purpose registers