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3. PROGRAM COUNTER (PC)
The program counter addresses program memory or a program. It is a 12-bit binary counter.
PC
PC
PC
11
10
Normally, the program counter is incremented by 1 each time an instruction is executed. When a branch
instruction or a subroutine call instruction is executed, however, the address specified in the operand field
is loaded into the program counter. If a skip instruction has been executed, the address of the instruction
following the skip instruction is specified, regardless of the contents of the skip instruction. If the specified
address contains a skip condition, the instruction following the skip instruction is regarded as being a NOP
instruction. That is, the NOP instruction is executed, and the address of the next instruction is specified.
If an interrupt request is accepted, one of addresses 1 to 4 (depending on the cause of the interrupt) is loaded
into the PC.
If a power-on reset or a CE reset is performed, the program counter is reset to address 0.
Table 3-1 Vector Addresses upon Interrupt Occurrence
Fig. 3-1 Program Counter
PC
PC
PC
9
8
7
6
12 bits
Priority
Interrupt cause
1
INT
pin
NC
2
Internal timer
3
V
pin
SYNC
4
Serial interface
PC
PC
PC
PC
5
4
3
Vector address
4H
3H
2H
1H
PD17062
PC
PC
2
1
0
25
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