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MB96300 Super Series Hardware Manual
2.4.4
Program Counter (PC)
The PC register is a 16-bit counter that indicates the low-order 16 bits of the memory
address of an instruction code to be executed by the CPU.
■ Program counter (PC)
The PC register is a 16-bit counter that indicates the low-order 16 bits of the memory address of an
instruction code to be executed by the CPU. The high-order eight bits of the address are indicated by the
program bank register (PCB).
The PC register is updated by a branch instruction, subroutine call instruction, interrupt or reset. Within a
linear program segment, the PC is incremented by the number of bytes of the last instruction.
The PC register can also be used as a base pointer for operand access.
Figure 2.4-9"Program counter" shows the program counter.
PCB
FE H
The reset address is fixed to the Boot ROM program start address of 0F:FC00
to FC00
and the PCB is initialized to 0F
H
In external vector mode a value specified by the reset vector on address FF:FFDC
the Boot ROM code execution. In internal vector mode the PCB and the PC are loaded with fixed values
defined by the product.
Figure 2.4-9 Program counter
PC
ABCD H
FEABCD H
.
H
CHAPTER 2 CPU
Next instruction to be executed
. At reset, the PC is initialized
H
is loaded when leaving
H
73
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