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PLC Communications
5-3
386/ATM Coprocessor User Manual
The PCCOMM service provides two types of functions:
•
IOREAD and IOWRITE access the 4 WX and 4 WY I/O points during
the I/O cycle of the PLC scan
•
PCREAD and PCWRITE access PLC memory during the Special
Function Module cycle of the PLC scan
The following sequence of events is an outline for using the PCCOMM
service to communicate to the local I/O points in the 386/ATM.
1.
Make sure that the 386ATM device driver is loaded when the 386/ATM
boots up.
2.
Write an application program that communicates with the PCCOMM
service.
Appendix B provides examples of application programs. The sequence of
events in the program are as follows.
1.
Open an unbuffered file stream with the name of PCCOMM.
2.
Build a command string to perform the function required.
3.
Send the command string to the open file stream.
4.
Read the response string from the file stream.
5.
Get the information from the response string.
Table 5-1
Maximum Words or Bits Transferred per PCCOMM Transaction
PCCOMM Operation
Maximum Transfer
IOREAD
4 words
IOWRITE
4 words
PCREAD/PCWRITE (V-mem, WX, etc.)
120 words
PCREAD/PCWRITE (CR, X, Y, etc.)
480 bits
Using PCCOMM
Application
Program I/O Bus
Communication
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