Automation Direct D0-DCM, Руководство пользователя

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Getting Started
User Application
Guidelines
RLL
Programming
for Communications
4–2
RLL Programming for Communications
DL05/06 Data Communications Module, 1st Edition, 08/05
PLC-to-PLC Communications
This chapter steps you through the development of a Relay Ladder Logic (RLL)
program to enable one PLC to communicate with another PLC. For the experienced
programmer of DirectLOGIC PLCs, the communication programs presented in this
chapter will be simple to follow. If you have never programmed a DirectLOGIC PLC,
you may want to refer to the DirectSOFT32 Programming Software User Manual
and the User Manual for your PLC for additional information.
NOTE: The programs described in this chapter are not used for communication
between a PC and a PLC. For PC-to-PLC communications, please see the product
documentation for the PC software you are using.
How RLL is Used for Communications
DirectSOFT32 Programming Software provides Read and Write instructions
(RX/WX) for PLC-to-PLC communication over a network. The Read and Write
instructions are part of the ladder logic program running in the CPU of the initiating,
or master, PLC. These instructions tell the initiating CPU to send a message over the
serial network to a responding, or slave, PLC. The initiating PLC’s Read or Write
communication finds its destination by the slave address of the responding PLC.
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Wr it
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Slave 1
Slave 3
Slave 2
Master DCM
NOTE: When all slave’s addresses are set to 0 (zero), the master D0–DCM can write
data to all slaves at the same time using the WX instruction. This is referred to as
“broadcast mode”. If this mode is used, the master DCM cannot use the RX
instruction to read data from individual slaves.