Let us consider the instruction JMP Label (PC← Label) and derive its execution control sequence. This unconditional jump instruction will load the program counter with the address of Label such that in the next fetch cycle, the instruction is fetched from the address given by Label.

In relative addressing (short and near jumps), what is stored in the instruction is not the absolute address of label but an offset from the PC, i.e., Label - PC. Note that PC will be pointing at the instruction following the JMP instruction. When the CPU executes the JMP instruction, it will add the content of PC to the offset stored in the instruction to get the actual address of Label, i.e. (Label-PC)+PC= Label.

The execution control sequence for the JMP Label instruction for the single-bus CPU is given in the following table:

Control Sequence	Active Signals
T4	PCout, Yin
T5	(offset-field-of-IR)out, ALU (C=A+B), Zin
T6	Zout, PCin, END

In T4, the content of PC is stored in the Y register. In T5, the offset field of the IR, which contains Label-PC, is put on the CPU bus and added with Y and the result is stored in Z. At this point Z will contain the actual address of Label. In T6, the content of the Z register, which is the address of Label, is stored in PC and the execution control sequence is terminated by the END signal.

The execution control sequence of the JMP Label instruction for the single-bus CPU is demonstrated in the next figure:

Fig. m300126.1 Execution Control Sequence for JMP Instruction in a Single-Bus CPU