12 Modbus Serial Communications; Din, -Din; Physical Layer - WEST P8700 User Manual

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12 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:
Parity:
Character format:
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.
59305, Issue 5 – March 2005
- DIN Controllers & Indicators - Product Manual
1200, 2400, 4800 (default), 9600 and 19,200 bps
None (default), Even, Odd
Always 8 bits per character.
Modbus Communications Page 93