C515A_9708 Datasheet, PDF (27/182 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Memory Organization
C515A
Port 0
Address/Data
XPAGE
Write I/O Data
to Port 2
Port 2
XRAM
I/O-Data
MCB02114
Figure 3-4
Use of Port 2 as I/O Port
At a write to port 2, the XRAM address in 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 FF30H.
MOV
MOV
MOV
MOVX
R0, #30H
P2, #0AAH
XPAGE, #0FFH
A, @R0
;
; P2 shows AAH and XPAGE contains AAH
; P2 still shows AAH but XRAM is addressed
; the contents of XRAM at FF30H is moved to accumulator
Semiconductor Group
3-8
1997-08-01