DAA - Revision history

Beannaich at 13:55, 25 May 2012

2012-05-25T13:55:49Z

Beannaich at 13:46, 25 May 2012

2012-05-25T13:46:46Z

Beannaich: Created page with ' +---+---+---+--------------+--------------+--------------+---------+ | N | H | C | Upper Nybble | Lower Nybble | Number Added | C After | +---+---+---+--------------+---------…'

2012-05-25T13:31:53Z

Created page with ' +---+---+---+--------------+--------------+--------------+---------+ | N | H | C | Upper Nybble | Lower Nybble | Number Added | C After | +---+---+---+--------------+---------…'

New page

+---+---+---+--------------+--------------+--------------+---------+
| N | H | C | Upper Nybble | Lower Nybble | Number Added | C After |
+---+---+---+--------------+--------------+--------------+---------+
| 0 | 0 | 0 | 9-0 | 0-9 | 00 | 0 |
| 0 | 0 | 0 | 0-8 | A-F | 06 | 0 |
| 0 | 1 | 0 | 0-9 | 0-3 | 06 | 0 |
| 0 | 0 | 0 | A-F | 0-9 | 60 | 1 |
| 0 | 0 | 0 | 9-F | A-F | 66 | 1 |
| 0 | 1 | 0 | A-F | 0-3 | 66 | 1 |
| 0 | 0 | 1 | 0-2 | 0-9 | 60 | 1 |
| 0 | 0 | 1 | 0-2 | A-F | 66 | 1 |
| 0 | 1 | 1 | 0-3 | 0-3 | 66 | 1 |
+---+---+---+--------------+--------------+--------------+---------+
| 1 | 0 | 0 | 0-9 | 0-9 | 00 | 0 |
| 1 | 1 | 0 | 0-8 | 6-F | FA | 0 |
| 1 | 0 | 1 | 7-F | 0-9 | A0 | 1 |
+---+---+---+--------------+--------------+--------------+---------+

== Instructions ==

DAA - $27 - 1 Machine Cycle

== Flags ==

Z: 1 if Accumulator is zero after operation; 0 otherwise
N: not affected
H: see instruction
C: see instruction

← Older revision		Revision as of 13:55, 25 May 2012
Line 1:		Line 1:
		+	{{Opcode}}
		+
	If an addition operation is performed between 15 (BCD) and 27 (BCD), simple decimal arithmetic gives this result:		If an addition operation is performed between 15 (BCD) and 27 (BCD), simple decimal arithmetic gives this result:

@@ Line 1: / Line 1: @@
- +---+---+---+--------------+--------------+--------------+---------+
+If an addition operation is performed between 15 (BCD) and 27 (BCD), simple decimal arithmetic gives this result:
- | N | H | C | Upper Nybble | Lower Nybble | Number Added | C After |
-  +---+---+---+--------------+--------------+--------------+---------+
- | 0 | 0 | 0 | 9-0          | 0-9          | 00           | 0       |
+  + 27
- | 0 | 0 | 0 | 0-8          | A-F          | 06           | 0       |
+   --
- | 0 | 1 | 0 | 0-9          | 0-3          | 06           | 0       |
- | 0 | 0 | 0 | A-F          | 0-9          | 60           | 1       |
- | 0 | 0 | 0 | 9-F          | A-F          | 66           | 1       |
+But when the binary representations are added in the Accumulator according to standard binary arithmetic.
- | 0 | 1 | 0 | A-F          | 0-3          | 66           | 1       |
-  | 0 | 0 | 1 | 0-2          | 0-9          | 60           | 1       |
+0101
- | 0 | 0 | 1 | 0-2          | A-F          | 66           | 1       |
+  + 0010 0111
- | 0 | 1 | 1 | 0-3          | 0-3          | 66           | 1       |
+   ---------
- +---+---+---+--------------+--------------+--------------+---------+
+1100 = $3C
- | 1 | 0 | 0 | 0-9          | 0-9          | 00           | 0       |
- | 1 | 1 | 0 | 0-8          | 6-F          | FA           | 0       |
+the sum is ambiguous. The DAA instruction adjusts this result so that the correct BCD representation is obtained:
- | 1 | 0 | 1 | 7-F          | 0-9          | A0           | 1       |
+1100
-  +---+---+---+--------------+--------------+--------------+---------+
+  + 0000 0110
 == Instructions ==
@@ Line 25: / Line 26: @@
   Z: 1 if Accumulator is zero after operation; 0 otherwise
   N: not affected
-  H: see instruction
+  H: 0
-  C: see instruction
+  C: 1 if N is 0 and A is greater than $99, 0 otherwise