4501 datasheet(15/116 Pages) RENESAS

15 / 116 page

4501 Group

Rev.3.01

2005.02.07

page 15 of 112

REJ03B0104-0301

(8) Program counter (PC)

Program counter (PC) is used to specify a ROM address (page and

address). It determines a sequence in which instructions stored in

ROM are read. It is a binary counter that increments the number of

instruction bytes each time an instruction is executed. However,

the value changes to a specified address when branch instructions,

subroutine call instructions, return instructions, or the table refer-

ence instruction (TABP p) is executed.

Program counter consists of PCH (most significant bit to bit 7)

which specifies to a ROM page and PCL (bits 6 to 0) which speci-

fies an address within a page. After it reaches the last address

(address 127) of a page, it specifies address 0 of the next page

(Figure 7).

Make sure that the PCH does not specify after the last page of the

built-in ROM.

(9) Data pointer (DP)

Data pointer (DP) is used to specify a RAM address and consists

of registers Z, X, and Y. Register Z specifies a RAM file group, reg-

ister X specifies a file, and register Y specifies a RAM digit (Figure

8).

When using port D, set the port D bit position to register Y certainly

and execute the SD, RD, or SZD instruction (Figure 9).

• Note

from reset.

Also, registers Z, X and Y are undefined in the RAM back-up. After

system is returned from the RAM back-up, set these registers.

Fig. 7 Program counter (PC) structure

Fig. 8 Data pointer (DP) structure

Fig. 9 SD instruction execution example

p5 p4 p3 p2 p1 p0

a6 a5 a4 a3 a2 a1 a0

Program counter

PCH

Specifying page

PCL

Specifying address

Z1 Z0 X3 X2 X1 X0 Y3 Y2 Y1 Y0

Data pointer (DP)

Specifying

RAM digit

Specifying RAM file

Specifying RAM file group

Set

Specifying bit position

Port D output latch

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