The X 86 Microprocessors: Architecture, Programming and Interfacing (8086 to Pentium) 2nd Edition by Pearson

THE HARDWARE STRUCTURE OF 8086 6-25

instruction with a LOCK prefix to cause the hardware LOCK signal to be asserted. For

example, if the 8086 wants 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 prefix 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 ...