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4513/4514 Group User’s Manual
HARDWARE
1-19
FUNCTION BLOCK OPERATIONS
(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).
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 9).
Fig. 7 Program counter (PC) structure
Fig. 8 Data pointer (DP) structure
Fig. 9 SD instruction execution example
Z1 Z0 X3 X2 X1 X0 Y3 Y2 Y1 Y0
Data pointer (DP)
Register Z (2)
Register X (4)
Register Y (4)
Specifying
RAM digit
Specifying RAM file
Specifying RAM file group
0101 1
D7
Set
Specifying bit position
Port D output latch
Register Y (4)
D5D6 D4 D0
p5 p4 p3 p2 p1 p0 a6 a5 a4 a3 a2 a1 a0
Program counter
PCH
Specifying page
PCL
Specifying address
p6