DAA (SPC700): Difference between revisions

Latest revision as of 08:18, 23 September 2024


Basic Info
Addressing Mode	Opcode	Length	Speed
Accumulator	DF	1 byte	3 cycles


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

DAA (Decimal Adjust for Addition) is an SPC700 instruction that BCD-corrects a sum:

If either the carry flag is set or the accumulator exceeds 0x99, add 0x60 to the accumulator and set the carry flag. This corrects the tens column (but perhaps not completely).
Then, if either the half-carry flag is set, or the lower nibble of the accumulator exceeds 0x09, add 0x06 to the accumulator. This corrects the ones column and possibly increments the tens column by one.

DAA assumes the value in the accumulator is encoded in binary/hexadecimal (with any value in the range $00 to $FF) because that is what the ADC command can output. But the inputs to ADC are supposed to be in BCD. After DAA, the accumulator value will be in BCD once again where both nybbles are in the range 0 to 9. The SPC700 has no decimal mode, so that is why this command is important when working with decimal data.

Syntax

DAA
DAA A

External Links

Official Super Nintendo development manual on DAA: Table C-14 in Appendix C-8 of Book I
page 3-8-2 of Book I, lbid
ares source code, SPC700::instructionDecimalAdjustAdd
anomie: https://github.com/yupferris/TasmShiz/blob/8fabc9764c33a7ae2520a76d80ed7220bb939f12/spc700.txt#L409
http://www.righto.com/2023/01/understanding-x86s-decimal-adjust-after.html?m=1

@@ Line 14: / Line 14: @@
 {| 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 31: / Line 31: @@
 |.
 |.
-|
+|Z
-|
+|C
 |}
-'''DAA''' (Decimal Adjust for Addition) is an [[SPC700]] instruction that performs the following:
+'''DAA''' (Decimal Adjust for Addition) is an [[SPC700]] instruction that [[BCD]]-corrects a sum:
+# If either the [[carry flag]] is set or the [[accumulator]] exceeds 0x99, add 0x60 to the accumulator and set the carry flag.  This corrects the tens column (but perhaps not completely).
+# Then, if either the [[half-carry flag]] is set, or the lower nibble of the accumulator exceeds 0x09, add 0x06 to the accumulator.  This corrects the ones column and possibly increments the tens column by one.
+DAA assumes the value in the accumulator is encoded in binary/hexadecimal (with any value in the range $00 to $FF) because that is what the [[ADC (SPC700)|ADC]] command can output.  But the inputs to ADC are supposed to be in BCD.  After DAA, the accumulator value will be in BCD once again where both nybbles are in the range 0 to 9.  The SPC700 has no [[decimal mode]], so that is why this command is important when working with decimal data.
-# If either the [[carry flag]] is set or the [[accumulator]] exceeds 0x99, 0x60 is added to the accumulator and the carry flag is set.
+==== Syntax ====
-# Then, if either the [[half-carry flag]] is set, or the lower nibble of the accumulator exceeds 0x09, 0x06 is added to the accumulator.
+<pre>
+DAA
+DAA A
+</pre>
 === See Also ===
 * [[DAS]]
-* [[BCD]]
+* [[SED]]
+* [[CLD]]
 === External Links ===
 * Official Super Nintendo development manual on DAA: Table C-14 in [https://archive.org/details/SNESDevManual/book1/page/n233 Appendix C-8 of Book I]
-* [https://archive.org/details/SNESDevManual/book1/page/n180 page 3-8-2 of Book I] lbid
+* [https://archive.org/details/SNESDevManual/book1/page/n180 page 3-8-2 of Book I], lbid
 * ares source code, SPC700::instructionDecimalAdjustAdd
+* anomie: https://github.com/yupferris/TasmShiz/blob/8fabc9764c33a7ae2520a76d80ed7220bb939f12/spc700.txt#L409
+* http://www.righto.com/2023/01/understanding-x86s-decimal-adjust-after.html?m=1
 [[Category:ASM]]
 [[Category:SPC700]]
 [[Category:Decimal Compensation Commands]]