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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 543210
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
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