Z8
®
CPU
User Manual
UM001604-0108 Instruction Description
182
Halt
Syntax
HALT
Instruction Format
Operation
The HALT instruction turns off the internal CPU clock, but not the XTAL oscillation. The
counter/timers and the external interrupts IRQ1, IRQ2, and IRQ3 remain active. The
devices are recovered by interrupts, either externally or internally generated.
In order to enter HALT mode, it is necessary to first flush the instruction pipeline to avoid
suspending execution in mid-instruction. You must execute a NOP immediately before the
execution of the HALT instruction.
Example
Assuming the Z8
®
CPU is in normal operation, the statements:
NOP
HALT
Op Codes: FF 7F
place the Z8 CPU into HALT mode.
Cycles
OPC
(Hex)
OPC 6 7F
Flag Description
C Unaffected
Z Unaffected
S Unaffected
V Unaffected
D Unaffected
H Unaffected
Note:
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