
218 THE x86 MICROPROCESSORS
to retain the bus until a string transfer is completed fully, it can use the instruction (say) LOCK
REP MOVSB. So the processor does not have to relinquish the bus after one bus cycle, as may
be the case if the LOCK prefi x is not used. Instead, the bus is retained until the complete string
operation is over.
We have discussed all the maximum mode pins of 8086 and the diagram, with all the
control signals, is shown in
Fig 6.25
6.5 | Instruction Cycle
Now, let us decide what we mean by the word ‘instruction cycle’. e time taken by the processor
to execute an instruction is called an instruction cycle, and it is specifi ...