4571 Datasheet, PDF (14/126 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4571 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 13).
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,
register X specifies a file, and register Y specifies a RAM digit
(Figure 14).
Register Y is also used to specify the port D bit position.
When using port D, set the port D bit position to register Y
certainly and execute the SD, RD, or SZD instruction (Figure
15).
• Note
Register Z of data pointer is undefined after system is released
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.
Program counter
p6 p5 p4 p3 p2 p1 p0 a6 a5 a4 a3 a2 a1 a0
PCH
Specifying page
PCL
Specifying address
Fig 13. Program counter (PC) structure
Data pointer (DP)
Z1 Z0 X3 X2 X1 X0 Y3 Y2 Y1 Y0
Register Y (4)
Specifying
RAM digit
Register X (4)
Specifying RAM file
Register Z (2)
Specifying RAM file group
Fig 14. Data pointer (DP) structure
Specifying bit position
Set
0001
Register Y (4)
D3 D2 D1 D0
1
Port D output latch
Fig 15. SD instruction execution example
Rev.1.02 May 25, 2007 Page 14 of 124
REJ03B0179-0102