15
15 – 37
Z:
Destination register
Yop:
Y operand
Xop:
X operand
COND: condition
Syntax:
[ IF cond ]
AR = yop – 1 ;
AF
Permissible yops
Permissible conds (see Table 15.9)
AY0
EQ LE
AC
AY1
NE NEG
NOT AC
AF
GT POS
MV
GE AV
NOT MV
LT
NOT AV
NOT CE
Example:
IF EQ AR = AY1 – 1 ;
Description:
Test the optional condition and if true, then decrement the
source operand by H#0001 and store in the destination location. If the
condition is not true then perform a no-operation. Omitting the condition
performs the decrement operation unconditionally. The source operand is
contained in the data register specified in the instruction.
Status Generated:
ASTAT:
7
6
5
4
3
2
1
0
SS
MV AQ AS
AC AV AN AZ
–
–
–
–
*
*
*
*
AZ
Set if the result equals zero. Cleared otherwise.
AN
Set if the result is negative. Cleared otherwise.
AV
Set if an overflow is generated. Cleared otherwise.
AC
Set if a carry is generated. Cleared otherwise.
Instruction Format:
Conditional ALU/MAC Operation, Instruction Type 9:
23 22 21 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
0 0 1 0 0 Z AMF Yop Xop 0 0 0 0 COND
AMF specifies the ALU or MAC operation. In this case,
AMF = 11000 for yop – 1 operation.
Note that the xop field is ignored for the decrement operation.
ALU
DECREMENT