BBC (SPC700): Difference between revisions

Revision as of 20:37, 24 July 2023


Basic Info
Addressing Mode	Opcode	Length	Speed
Direct Page	13	3 byte	when condition is false: 5 cycles when condition is true: 7 cycles
Direct Page	33	3 byte	when condition is false: 5 cycles when condition is true: 7 cycles
Direct Page	53	3 byte	when condition is false: 5 cycles when condition is true: 7 cycles
Direct Page	73	3 byte	when condition is false: 5 cycles when condition is true: 7 cycles
Direct Page	93	3 byte	when condition is false: 5 cycles when condition is true: 7 cycles
Direct Page	B3	3 byte	when condition is false: 5 cycles when condition is true: 7 cycles
Direct Page	D3	3 byte	when condition is false: 5 cycles when condition is true: 7 cycles
Direct Page	F3	3 byte	when condition is false: 5 cycles when condition is true: 7 cycles


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

BBC (Branch on Bit Clear) is an SPC700 instruction that performs a branch when a bit in the direct page is clear. The index to the direct page byte that bit lives in is the first operand byte. Which bit within that byte is specified by the top 3 bits of the opcode. The target relative address to jump to is the second operand byte.

In assembly source, the two operands appear in the same order that they do in the instruction stream.

External Links

Official Super Nintendo development manual on BBC: Appendix C-8 of Book I

@@ Line 78: / Line 78: @@
 |}
-'''BBC''' (Branch on Bit Clear) is an [[SPC700]] instruction that performs a branch when a bit in the [[direct page]] is clear.  The direct page byte that bit lives in is the first operand.  The bit within that byte is a function of the high nibble of the opcode.  The target relative address to jump to is the second operand.
+'''BBC''' (Branch on Bit Clear) is an [[SPC700]] instruction that performs a branch when a bit in the [[direct page]] is clear.  The index to the direct page byte that bit lives in is the first operand byte.  Which bit within that byte is specified by the top 3 bits of the opcode.  The target relative address to jump to is the second operand byte.
+In assembly source, the two operands appear in the same order that they do in the instruction stream.
 === See Also ===