SBC (SPC700): Difference between revisions

Latest revision as of 08:56, 19 September 2024


Basic Info
Addressing Mode	Opcode	Length	Speed
Immediate	A8	2 bytes	2 cycles
Implied Indirect (type 1)	A6	1 byte	3 cycles
Direct Page	A4	2 bytes	3 cycles
Direct Page Indexed by X	B4	2 bytes	4 cycles
Absolute	A5	3 bytes	4 cycles
Absolute Indexed by X	B5	3 bytes	5 cycles
Absolute Indexed by Y	B6	3 bytes	5 cycles
Direct Page Indexed by X	A7	2 bytes	6 cycles
Direct Page Indirect Indexed by Y	B7	2 bytes	6 cycles
Implied Indirect (type 1)	B9	1 byte	5 cycles
Direct Page	A9	3 bytes	6 cycles
Direct Page Immediate	B8	3 bytes	5 cycles


Flags Affected
N	V	P	B	H	I	Z	C
N	V	.	.	H	.	Z	C

SBC (Subtract) is an SPC700 instruction that subtracts the right operand and the inverse of the carry flag from the left operand. Often, the left operand is the accumulator.

The operands are stored in the instruction stream in the opposite order they appear in the assembler source. In the assembler source, the operand on the right is the source and the operand on the left is the destination.

Syntax

SBC A, #imm
SBC A, (X)
SBC A, dp
SBC A, dp+X
SBC A, !abs
SBC A, !abs+X
SBC A, !abs+Y
SBC A, [dp+X]
SBC A, [dp]+Y
SBC (X), (Y)
SBC dp<d>, dp<s>
SBC dp, #imm

Unlike the 65c816, the SPC700 has no decimal mode, so the subtraction is always done in binary/hexadecimal. Use DAS after subtracting BCD-encoded data to repair it back to BCD.

External Links

Official Super Nintendo development manual on SBC: Table C-7 in Appendix C-5 of Book I
anomie: https://github.com/yupferris/TasmShiz/blob/master/spc700.txt#L559

@@ Line 80: / Line 80: @@
 |[[Carry Flag|C]]
 |+
-|
+|N
-|
+|V
 |.
 |.
-|
+|H
 |.
-|
+|Z
-|
+|C
 |}
@@ Line 109: / Line 109: @@
 SBC dp, #imm
 </pre>
+Unlike the [[65c816]], the SPC700 has no [[decimal mode]], so the subtraction is always done in binary/hexadecimal. Use [[DAS]] after subtracting [[BCD]]-encoded data to repair it back to BCD.
 === See Also ===