INSTRUCTION DESCRIPTIONS
A - 248 INSTRUCTION SET DETAILS MOTOROLA
Operation: Assembler Syntax:
LC ➞ TEMP; X:ea ➞ LC REP X:ea
Repeat next instruction until LC=1
TEMP ➞ LC
LC ➞ TEMP; X:aa ➞ LC REP X:aa
Repeat next instruction until LC=1
TEMP ➞ LC
LC ➞ TEMP; Y:ea ➞ LC REP Y:ea
Repeat next instruction until LC=1
TEMP ➞ LC
LC ➞ TEMP; Y:aa ➞ LC REP Y:aa
Repeat next instruction until LC=1
TEMP ➞ LC
LC ➞ TEMP; S ➞ LC REP S
Repeat next instruction until LC=1
TEMP ➞ LC
LC ➞ TEMP; #xxx ➞ LC REP #xxx
Repeat next instruction until LC=1
TEMP ➞ LC
Description: Repeat the single-word instruction immediately following the REP
instruction the specified number of times. The value specifying the number of times the
given instruction is to be repeated is loaded into the 16-bit loop counter (LC) register.
The single-word instruction is then executed the specified number of times, decrement-
ing the loop counter (LC) after each execution until LC=1. When the REP instruction is in
effect, the repeated instruction is fetched only one time, and it remains in the instruction
register for the duration of the loop count. Thus, the REP instruction is not interrupt-
ible (sequential repeats are also not interruptible). The current loop counter (LC) value is
stored in an internal temporary register. If LC is set equal to zero, the instruction is
repeated 65,536 times. The instruction’s effective address specifies the address of the
value which is to be loaded into the loop counter (LC). All address register indirect
addressing modes may be used. The absolute short and the immediate short addressing
modes may also be used. The four MS bits of the 12-bit immediate value are zeroed to
form the 16-bit value that is to be loaded into the loop counter (LC).
REP Repeat Next Instruction REP