LSR (SPC700): Difference between revisions

Latest revision as of 00:04, 15 August 2024


Basic Info
Addressing Mode	Opcode	Length	Speed
Accumulator	5C	1 byte	2 cycles
Direct Page	4B	2 bytes	4 cycles
Direct Page Indexed by X	5B	2 bytes	5 cycles
Absolute	4C	3 bytes	5 cycles


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

LSR (Logical Shift Right) is an SPC700 instruction that shifts all 8 bits of its operand one bit to the right, dividing it by two. The least significant bit is shifted into the carry flag. A zero is shifted into the most significant bit.

The official manual has the bit shift operators for LSR pointing the wrong way.

Syntax

LSR A
LSR dp
LSR dp+X
LSR !abs

LSR is a fast alternative to DIV when dividing by a power of two.

External Links

Official Super Nintendo development manual on LSR: Appendix C-7 of Book I
anomie: https://github.com/yupferris/TasmShiz/blob/master/spc700.txt#L457

@@ Line 22: / Line 22: @@
 |5 cycles
 |+
-|
+|[[Absolute Addressing | Absolute]]
 |4C
 |3 bytes
@@ Line 29: / Line 29: @@
 {| class="wikitable" style="float:right;clear:right;width:30%"
-!colspan="8"|Flags Clobbered
+!colspan="8"|Flags Affected
+|+
+|[[Negative Flag|N]]
+|[[Overflow Flag|V]]
+|[[Direct Page Flag|P]]
+|[[Break Flag|B]]
+|[[Half-Carry Flag|H]]
+|[[Interrupt Enable Flag|I]]
+|[[Zero Flag|Z]]
+|[[Carry Flag|C]]
 |+
 |N
-|V
-|P
-|B
-|H
-|I
-|Z
-|C
-|+
-|
 |.
 |.
@@ Line 46: / Line 46: @@
 |.
 |.
-|
+|Z
-|
+|C
 |}
-'''LSR''' (Logical Shift Right) is an [[SPC700]] instruction that shifts its operand one bit to the right, dividing it by two.  The least significant bit is shifted into the [[carry flag]].  A zero is shifted into the most significant bit.
+'''LSR''' (Logical Shift Right) is an [[SPC700]] instruction that shifts all 8 bits of its operand one bit to the right, dividing it by two.  The least significant bit is shifted into the [[carry flag]].  A zero is shifted into the most significant bit.
 The official manual has the bit shift operators for LSR pointing the wrong way.
+==== Syntax ====
+<pre>
+LSR A
+LSR dp
+LSR dp+X
+LSR !abs
+</pre>
+[[File:lsr_spc.png]]
+LSR is a fast alternative to [[DIV]] when dividing by a power of two.
 === See Also ===
@@ Line 60: / Line 72: @@
 === External Links ===
 * Official Super Nintendo development manual on LSR: [https://archive.org/details/SNESDevManual/book1/page/n232 Appendix C-7 of Book I]
+* anomie: https://github.com/yupferris/TasmShiz/blob/master/spc700.txt#L457
 [[Category:ASM]]
 [[Category:SPC700]]
 [[Category:Shift Rotation Commands]]