4559 datasheet(20/148 Pages) RENESAS

20 / 148 page

Rev.1.04

Aug 23, 2007

Page 20 of 146

REJ03B0188-0104

4559 Group

(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 reference 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

specifies 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 18).

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,

(Figure 19).

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

certainly and execute the SD, RD, or SZD instruction (Figure

20).

•Note

from reset.

Also, registers Z, X and Y are undefined in the power down

mode. After system is returned from the power down mode, set

these registers.

Fig 18. Program counter (PC) structure

Fig 19. Data pointer (DP) structure

Fig 20. SD instruction execution example

PCH

Specifying page

Program counter (PC)

PCL

Specifying address

Data pointer (DP)

X2 X1 X0 Y3

Z1 Z0 X3

Y2 Y1 Y0

Specifying RAM digit

Specifying RAM file

Specifying RAM file group

Specifying bit position

Set

Port D output latch

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