Despatch P1400+ Temperature Controller User Manual

Page 63

SECTION 10: 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/

http://www.modbus.org/

10.1 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.