Unconditional jump - jump instruction , Electrical Engineering

Unconditional Jump

JMP ( Unconditional Jump ) Instruction: This  instruction is used to transfer  the execution to the  specified  memory  address unconditionally ( does not check any condition before jump).  It is  normally  used to create an indefinite  loop. The  instruction format is

                            JMP 16 bit memory address

Actually it copies  the specified  memory address into the  program counter register. Hence the  microprocessor reads  the next  instruction from the address  stored in the program  counter. Now as  usual  the contains  of the  program  counter register  starts  incrementing by  one. Program executes sequentially until it encounters any other  branch  instruction.

See followings   example to  understand  the working  of JMP  instruction.

Note: You  must have noticed that Sex codes  of IN  and OUT  instruction  are written  at two  consecutive  memory  locations and Hex  codes  of JMP instruction  are written at  three  consecutive  memory  locations. Without going  into the  details of the Hex  codes and size of the instruction at this moment ( which will be  discussed later in this chapter) let us concentrate on the working  of the JMP  instruction.

In the  above program the instruction JMP  20502H will  transfer  the execution back to the first instruction which is stored  at 2050H and keep on repeating the  task by  creating  an indefinite  loop.

The  above  program may be  written  as shown  below using labels when written  using  assembler. In laboratory using microprocessor  kit one has to the hex  codes( programming techniques will be explained in detail in chapter4).

The label  represent the  memory  address of the instruction written  along with  it. In the above  program the label  START represents the  memory  address 2050H where IN  instruction is stored. It is referred  by JMP  instruction  written at memory  location 2054H.

Posted Date: 4/5/2013 1:07:15 AM | Location : United States







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