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3.2.5
Program counter (PC)
The program counter (PC) is a 16-bit counter indicating the lower 16 bits of the address
for the next instruction code to be executed by the CPU.
I Program counter (PC)
The program bank register (PCB) indicates the higher 8 bits of addresses where the next instruction code to
be executed by the CPU is stored; the program counter (PC) indicates the lower 16 bits. As shown in Figure
3.2-15 "Program counter (PC)", the actual addresses are combined into 24 bits.
The program counter (PC) is updated by the execution of the conditional branch instruction, the subroutine
call instruction, by an interrupt or reset, etc.
The program counter (PC) can also be used as the base pointer when reading the operand.
Upper 8-bit
PCB
Note:
Neither the program counter (PC) nor the program bank register (PCB) can be rewritten
directly by a program (such as MOV PC and #FF).
Figure 3.2-15 Program counter (PC)
Lower 16-bit
FE
ABCD
PC
H
H
FEABCD
Instruction executed next
H
CHAPTER 3 CPU
45
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