C509-L_97 SIEMENS [Siemens Semiconductor Group], C509-L_97 Datasheet - Page 67

• Manufacturer Part Number: C509-L_97
• Description: 8-Bit CMOS Microcontroller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

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 AA H . A byte shall be fetched from XRAM at address F830 H .
MOV
MOV
MOV
MOVX
Semiconductor Group
R0, #30H
P2, #0AAH
XPAGE, #0F8H
A, @R0
Write I/O Data
to Port 2
XPAGE
Port 0
Port 2
;
; P2 shows AAH
; P2 still shows AAH but XRAM is addressed
; the contents of XRAM at F830H is moved to accumulator
4-15
XRAM
External Bus Interface
MCB02114
Address/Data
I/O-Data
1997-10-01
C509-L