GE GFK0579B Scanner User Manual


 
3
Remote I/O Scanner User’s Manual – July 199250
Using Option Modules in a Remote Drop
PCMs (Programmable Coprocessor Modules), GDS (Graphics Display Coprocessor
Modules), and ADS (Alphanumeric Display Coprocessor Modules) can be located in a
remote drop.
These option modules look at the Remote I/O Scanner as though it were a Series
90–70 PLC CPU. They can read and write to any locations in the Remote I/O Scanner’s
internal %I, %AI, %Q, %AQ, and %R memories, including those portions of memory
that are outside the range configured for data transfer with the system host.
The Remote I/O Scanner’s %R memory is NOT used for data transferred with the
CPU, but it can be freely accessed by a PCM, GDS, or ADS module in the remote drop.
Accessing the Host CPU from Option Modules in a Remote Drop
When used in a remote drop, a PCM, GDS, or ADS module does not have direct access
to host CPU memory; to read or write host memory, the data must be transferred
through the configured memory area of the Remote I/O Scanner. The area used
should not correspond to a physical I/O module; it should correspond to an unused
portion of the remote drop I/O map configured for the remote drop.
Extending the I/O map of a remote drop will cause the Genius message to increase in
size, and will therefore increase the Genius bus scan time. Gaps may be anywhere in
the I/O map, but if they are added to the end, the corresponding I/O references cannot
be used for any other purpose by either the host or the Remote I/O Scanner.
Reading Host Data from an Option Module
% Q
% AQ
a44887
PCM, GDS
OR ADS
HOST
CPU
REMOTE I/O
SCANNER
MEMORIES
READ
MEMORIES
OUTPUT
MODULES
GENIUS
MESSAGE
% Q
% AQ