UPD17015 datasheet(15/120 Pages) NEC

15 / 120 page

µPD17015

2.3

PROGRAM COUNTER

Fig. 2-3 shows the configuration of the program counter.

As shown in Fig. 2-3, the program counter consists of a 11-bit binary counter.

The program counter is used to specify an address in program memory.

Fig. 2-3 Program Counter Configuration

MSB

LSB

11 bits

2.4

PROGRAM FLOW

The execution flow of a program is controlled with the program counter, which specifies an address in program

memory. This section describes the operation of several types of instructions.

Fig. 2-4 shows the value set in the program counter when each instruction is executed.

2.4.1

Direct branch (“BR addr”)

A direct branch instruction can branch to all addresses of program memory, 0000H to 05F7H.

2.4.2

Subroutines

To call a subroutine, a direct subroutine call (“CALL addr”) is used.

A direct subroutine call instruction can call a subroutine starting at any address in program memory, 0000H to

05F7H.

RET or RETSK instruction is used as the return instruction from a subroutine.

Fig. 2-4 Program Counter Value When Each Instruction Is Executed

CALL

RET

RETSK

addr

Instruction

Value of program counter

Program counter

At power-on reset or CE reset

Instruction operand (addr)

Contents of address stack register

(return address)

UPD17015 Datasheet(PDF) 15 Page - NEC