NEC PD17062 - Manual (Page 25)

25
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PD17062
3. PROGRAM COUNTER (PC)
The program counter addresses program memory or a program. It is a 12-bit binary counter.
Fig. 3-1 Program Counter
PC
11
PC
9
PC
10
PC
8
PC
6
PC
7
PC
5
PC
3
PC
4
PC
2
PC
0
PC
1
12 bits
Priority Interrupt cause Vector address
1 INT
NC
pin 4H
2 Internal timer 3H
3 V SYNC pin 2H
4 Serial interface 1H
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