C509-L_97 Datasheet, PDF (67/290 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

External Bus Interface
C509-L
Port 0
Address/Data
XPAGE
Write I/O Data
to Port 2
Port 2
XRAM
I/O-Data
MCB02114
Figure 4-6
Usage of Port 2 as I/O Port
At a write to port 2, the XRAM address in the XPAGE register will be overwritten because of the
concurrent write to port 2 and XPAGE register. So, whenever XRAM is used and the XRAM address
differs from the byte written to port 2 latch it is absolutely necessary to rewrite XPAGE with the page
address.
Example:
I/O data at port 2 shall be AAH. A byte shall be fetched from XRAM at address F830H.
MOV
R0, #30H
;
MOV
P2, #0AAH
; P2 shows AAH
MOV
XPAGE, #0F8H
; P2 still shows AAH but XRAM is addressed
MOVX A, @R0
; the contents of XRAM at F830H is moved to accumulator
Semiconductor Group
4-15
1997-10-01