4559 Datasheet, PDF (20/148 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

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,
register X specifies a file, and register Y specifies a RAM digit
(Figure 19).
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
20).
Program counter (PC)
p6 p5 p4 p3 p2 p1 p0 a6 a5 a4 a3 a2 a1 a0
PCH
Specifying page
PCL
Specifying address
Fig 18. 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
• Note
Register Z of data pointer is undefined after system is released
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.
Register Z (2)
Specifying RAM file group
Fig 19. Data pointer (DP) structure
Specifying bit position
Set
0001
Register Y (4)
D3 D2 D1 D0
1
Port D output latch
Fig 20. SD instruction execution example
Rev.1.04 Aug 23, 2007 Page 20 of 146
REJ03B0188-0104