Chapter 7 Communication function
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7.4.4 Specifications of MODBUS communication driver
It is communication specifications for communication via MODBUS protocol through GLOFA PLC of Cnet Ver. 2.0 set
to other company’s dedicated mode for the service. Application of MODBUS communication in Gm7 series from
other models of Cnet I/F modules. Please refer to 8.3 MODBUS protocol communication in GM7 series manual
for details.
MODBUS communication function is available only in Cnet I/F module Ver.2.0 or later.
Cnet I/F module operates as a server only in MODBUS, however, client operation is unavailable.
For MODBUS operation, download MODBUS.lib file first to Cnet I/F module via Frame Editor.
Operation mode of Cnet I/F module is to be set to other company’s dedicated mode.
ASCII/RTU modes among MODBUS protocols are supported simultaneously.
Basic parameters such as communication speed, station No., etc shall be set as agreed with the
communication specification of external devices.
Separate operation for each RS-232C/RS422 channel is available.
1)
Basic specification
Character protocol: Start/Stop/Data/Parity setting available(using Frame Editor)
Communication speed : 300 ~ 38400 BPS available
Channel operation : Stand-alone/Interlocking operation available for RS-232C/RS-422 channels.
Communication mode: HEX communication(RTU Mode), ASCII communication(ASCII Mode)
Frame check: CRC check(RTU Mode), LRC check(ASCII Mode)
Station No.area : 1 ~ 31 station available (station 0 unavailable)
Data length : Reading/Writing of max.120 bytes available.
ASCII mode : Communication via ASCII data.
- Error check through LRC
- Frame structure(ASCII data)
Type
Start (:)
Address
Function
Data
LRC
End(CR LF)
Size
1 byte
2 bytes
2 bytes
n bytes
2 bytes
2 bytes
RTU mode : Communication via HEX data.
- Error check through 16 bit CRC
- Frame structure(HEX data)
Type Start
Address
Function
Data CRC End
Size
T4 idle
1 byte
1 bytes
n bytes
2 bytes
T4 idle