Automation Direct D2-DCM, Руководство пользователя

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C–2
Using the D2–DCM with MODBUS
Data Communications Module, 2nd Edition, 2/03
Introduction
The D2–DCM can be used as a slave interface to a network using the MODBUS RTU protocol.
To use the D2–DCM with MODBUS, your host software must send a MODBUS function code
and a MODBUS address to specify a PLC memory location that is understood by the D2–DCM.
What's the status of Y0?
Host sends a
MODBUS request...
D2-DCM responds
Y0 is ON"
... D2–DCM
responds
with data
It would be quite difficult to discuss all of the ins and outs of MODBUS in this document.
Instead, the purpose of this Appendix is to:
D
provide a quick overview of MODBUS Data Types and Function Codes.
D
how to determine the proper MODBUS address necessary to allow the host
software to access various memory locations in the DL205 system.
One key point to remember is that not all host software packages using MODBUS drivers
operate exactly the same way. That is, there are a couple of different ways to achieve the
same result, especially when it comes to specifying the needed address for the PLC memory
location.
Therefore, it is important that you follow the instructions for your particular software
package or network master.
How Does the
D2–DCM work with
MODBUS?