C515C_9711 Datasheet, PDF (31/268 Pages) Siemens Semiconductor Group – 8-Bit CMOS Microcontroller

Memory Organization
C515C
Port 0
Write
I/O Data
to Port 2
XPAGE
Port 2
XRAM
CAN-Controller
Address/Data
I/O Data
MCS02763
Figure 3-4
Use of Port 2 as I/O Port
At a write to port 2, the XRAM/CAN controller 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 F830H.
MOV
MOV
MOV
MOVX
R0, #30H
P2, #0AAH
XPAGE, #0F8H
A, @R0
;
; P2 shows AAH and XPAGE contains AAH
; P2 still shows AAH but XRAM is addressed
; the contents of XRAM at F830H is moved to accumulator
Semiconductor Group
3-8
1997-11-01