XBA: Difference between revisions

Latest revision as of 15:12, 11 August 2024


Basic Info
Addressing Mode	Opcode	Length	Speed
Implied (type 1)	EB	1 byte	3 cycles


Flags Affected
N	V	M	X	D	I	Z	C
N	.	.	.	.	.	Z	.

XBA is a 65c816 instruction that exchanges the high byte (B) and low byte (typically called A) of the C accumulator. It works even in 6502 emulation mode. In 65816 native mode, its standard mnemonic is still "XBA" even when the accumulator is 16-bits wide. An alternative mnemonic is "SWA."

XBA can be used to convert big endian data to little endian and vice versa. XBA appears to be the only way to access the high B byte when the M flag is set.

The negative flag will match the most significant bit of the new low byte (A) of the accumulator. The zero flag will be set if and only if the new low byte (A) of the accumulator is zero, otherwise it is cleared.

Syntax

XBA
SWA

Even though the hidden B byte is colloquially considered to be second accumulator, XBA still isn't considered to use accumulator addressing.

External Links

Eyes & Lichty, page 524 on XBA
Labiak, page 204 on XBA
snes9x implementation of XBA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L3261
undisbeliever on XBA: https://undisbeliever.net/snesdev/65816-opcodes.html#xba-exchange-the-b-and-a-accumulators
Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.10.3

@@ Line 1: / Line 1: @@
-'''XBA''' is an instruction that exchanges the high byte (B) and low byte (typically called A) of the [[C accumulator]].  It works even in [[6502 emulation mode]].  In [[65816 native mode]], its mnemonic is still "XBA" even when the accumulator is 16-bits wide.
+{| class="wikitable" style="float:right;clear:right;width:40%"
+!colspan="8"|Basic Info
+|+
+|'''Addressing Mode'''
+|'''Opcode'''
+|'''Length'''
+|'''Speed'''
+|+
+|[[Implied]] (type 1)
+|EB
+|1 byte
+|3 cycles
+|}
 {| class="wikitable" style="float:right;clear:right;width:30%"
-!colspan="8"|Flags Clobbered
+!colspan="8"|Flags Affected
+|+
+|[[Negative Flag|N]]
+|[[Overflow Flag|V]]
+|[[M Flag|M]]
+|[[X Flag|X]]
+|[[Decimal Flag|D]]
+|[[I Flag|I]]
+|[[Zero Flag|Z]]
+|[[Carry Flag|C]]
 |+
 |N
-|V
+|.
-|M
+|.
-|X
+|.
-|D
+|.
-|I
+|.
 |Z
-|C
+|.
-|+
-|
-|
-|
-|
-|
-|
-|
-|
 |}
+'''XBA''' is a [[65c816]] instruction that exchanges the high byte (B) and low byte (typically called A) of the [[C accumulator]].  It works even in [[6502 emulation mode]].  In [[65816 native mode]], its standard mnemonic is still "XBA" even when the accumulator is 16-bits wide.  An alternative mnemonic is "SWA."
+XBA can be used to convert [[big endian]] data to [[little endian]] and vice versa.  XBA appears to be the only way to access the high B byte when the [[M flag]] is set.
+The [[negative flag]] will match the most significant bit of the new low byte (A) of the accumulator.
+The [[zero flag]] will be set if and only if the new low byte (A) of the accumulator is zero, otherwise it is cleared.
+==== Syntax ====
+<pre>
+XBA
+SWA
+</pre>
+Even though the hidden B byte is colloquially considered to be second accumulator, XBA still isn't considered to use [[accumulator addressing]].
+[[File:xba.png]]
+=== See Also ===
+* [[XCE]]
+* [[XCN]]
+* [[SWAP]]
+=== External Links ===
+* [[Eyes & Lichty]], [https://archive.org/details/0893037893ProgrammingThe65816/page/524 page 524] on XBA
+* [[Labiak]], [https://archive.org/details/Programming_the_65816/page/n214 page 204] on XBA
+* snes9x implementation of XBA: https://github.com/snes9xgit/snes9x/blob/master/cpuops.cpp#L3261
+* undisbeliever on XBA: https://undisbeliever.net/snesdev/65816-opcodes.html#xba-exchange-the-b-and-a-accumulators
+* Clark, Bruce. http://www.6502.org/tutorials/65c816opcodes.html#6.10.3
 [[Category:ASM]]
+[[Category:65c816 additions]]
+[[Category:Exchange Instructions]]
+[[Category:One-byte Instructions]]
+[[Category:Implied Instructions]]
+[[Category:Three-cycle Instructions]]