PLC Communications
5-10
386/ATM Coprocessor User Manual
Communicating during PLC Scan: Special Function Cycle (continued)
Example programs are included in Appendix B. Source code for the
examples is supplied on the 386/ATM device driver diskette.
Consider the following when reading or writing data.
•
The PLC input scan, ladder execution, loop execution, or special
function logic may overwrite any value written by PCWRITE. Ensure
that all systems software and hardware are coordinated so that they
work together.
Care should be taken when using PCWRITE to send data to word
memory areas. Unlike discrete memory points, word memory areas
can be overwritten even if they are forced.
•
All data and address values used in communications with PCCOMM are
in decimal (i.e., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12).
•
When reading or writing a discrete memory type, the data will be either
1 or 0.
Address for all memory types start with 1, with the exception of DCP,
which starts with address 0.
The format for DCP addressing is:
<drum_number> <step_number>
where
drum_number
is 1 based (1 through n) and
step_number
is 0
through 15.
Example:
Event drum 1, step 1 uses address 16 (base 10).
Event drum 1, step 2 uses address 17 (base 10).
Event drum 2, step 1 uses address 32 (base 10).
Event drum 2, step 2 uses address 33 (base 10).
Notes Concerning
Writing to Memory
Locations
CAUTION
!
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