West Control Solutions 8700+ - Manual (Page 126)

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- DIN Controllers & Indicators - Product Manual
59305, Issue 7
– March 2014 Modbus Communications Page 121
13 Modbus Serial Communications
All models support the Modbus RTU communication protocol. Some models also support an
ASCII communication protocol. Where both Modbus and ASCII are supported, the protocol to
be used is selected from Configuration Mode. The RS485 Communications Module must be
fitted into Option Slot A in order to use serial communications.
Refer to the relevant Model Group Section for the ASCII and Modbus Application Layer
(parameter address/ident information).
For a complete description of the Modbus protocol refer to the description provided at
http://www.modicon.com/ or http://www.modbus.org/
Physical Layer
The Base address, bit rate and character format are configured via the front panel in
Configuration Mode or by using the PC Configurator software.
Physical layer configuration settings possible are:
Data rate: 1200, 2400, 4800 (default), 9600 and 19,200 bps
Parity: None (default), Even, Odd
Character format: Always 8 bits per character.
The transmitter must not start transmission until 3 character times have elapsed since
reception of the last character in a message, and must release the transmission line within 3
character times of the last character in a message.
Note:
Three character times = 1.5ms at 19200, 3ms at 9600, 6ms at 4800, 12ms at 2400 and
24ms at 1200 bps.