Instruction Set
4-140
LOCK* Lock the Bus
LOCK
What It Does
The LOCK prefix asserts the LOCK signal for the specified instruction to prevent an external
master from requesting the bus.
Syntax
Description
LOCK is a prefix for a single instruction. On 186 processors with a LOCK pin assignment,
the LOCK pin is asserted for the duration of the prefixed instruction. The LOCK prefix may
be combined with the segment override and/or REP prefix.
Operation It Performs
Flag Settings After Instruction
Instruction prefixes do not affect the flags. See the instruction being prefixed for the flag
values.
Tips
The LOCK pin will assert for the entire repeated instruction.
LOCK prevents DMA cycles until the entire LOCK instruction is complete (this includes a
LOCK REP string instruction).
LOCK prevents the processor from acknowledging a HOLD or taking an interrupt except
for a nonmaskable interrupt.
Related Instructions
* – The external LOCK pin is only available on some members of the Am186 and Am188 family of microcontrollers.
However, LOCK internal logic is still in effect on parts without the LOCK pin.
Form
Prefix
to
Opcode
Description
Clocks
Am186 Am188
LOCK
F0
Asserts LOCK during an instruction execution
1
1
If you want to
See
Copy a component to a register or to a location in memory
MOV
Repeatedly execute a single
string instruction
REP
Exchange one component with another component
XCHG
LOCK
instr
assert LOCK#
execute(
instruction)
de-assert LOCK#
Содержание Am186 Series
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