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5.3
Communicating with the PLC Scan: Special Function Cycle
Description
386/ATM Coprocessor User Manual
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The PCREAD and PCWRITE commands allow you to gain access to various
types of memory in your PLC. The naming conventions used are from the
PLC perspective. (See Figure 5-4.) For instance, PCWRITE passes
information to the PLC, while PCREAD requests information from the PLC.
The memory types are categorized as:
•
Word access: VMEM, WX, WY, TCC, TCP, DSC, DCP, STW, DCP, KMEM
•
Discrete access: XREG, YREG, CREG
Consult your PLC programming manual for descriptions of each of the
above memory types.
Internal
diagnostics
I/O update
Relay
ladder
logic
Special
function
module
access
COMM
port
access
PLC CPU
Figure 5-4 PLC Scan: Special Function Cycle
PC COMM
Serial port
Serial
ports
PLC Communications
Application
Serial
1 or 2
386/ATM
I003101
5-7
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