4/17/98 6-89 Addressing Modes and Data Types
The following table shows the possible actions that may occur during the DA instruction, related
to the input conditions.
: The largest digit that could result from adding two BCD digits that caused the AC flag to
be set is 3. This is with an ADDC instruction where 9 + 9 + 1 (the carry flag) = 13 hex.
** : The largest digit that could result in the upper nibble of a value by adding two BCD bytes,
with no carry from the bottom nibble (the AC flag = 0) is 2. For instance, 98 hex + 97 hex = 12F
hex.
*** : The largest digit that could result in the upper nibble of a value by adding two BCD bytes,
with a carry from the bottom nibble (the AC flag = 1) is 3. For instance, 99 hex + 99 hex = 132 hex.
Table 6.6
Low nibble
(bits 3-0)
AC
Carry to
high
nibble
High
nibble
(bits 7-4)
Initial
C flag
Number
added to
value
Resulting
C flag
0 - 9 0 0 0 - 9 0 00 0
A - F 0 1 0 - 8 0 06 0
0 - 3 * 1 0 0 - 9 0 06 0
0 - 9 0 0 A - F 0 60 1
A - F 0 1 9 - F 0 66 1
0 - 3 * 1 0 A - F 0 66 1
0 - 9 0 0 0 - 2 ** 1 60 1
A - F 0 1 0 - 2 ** 1 66 1
0 - 3 * 1 0 0 - 3 *** 1 66 1
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