Fairford Electronics QFE Series, Manual

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Modbus
page 6-5
5MC
FD510007
6 The Modbus Protocol
6.1 Overview
The 5MC has built in serial communications this has been changed from Version 55 onwards
to be a compatible subset of the widely recognised Modbus RTU protocol (slave).
The serial communications is accessible from the keypad connector or with an additional
interface card (RS485) the 5MC may be connected to a PC or suitable PLC network.
6.2 Quick Start
Work should only be carried out on the 5MC with all electrical power disconnected
1) Communication settings
a) 9600 baud, 8 databits, 1 stop bit, no parity
b) network station number = 1
2) Before Connecting a Comms interface use the standard keypad to make any changes
for your bus system.
a) Set parameter 1 to the required network station number (slave address) now
unless station 1 is spare on the network.
b) If not continously polling the unit at least once every 2 seconds
set PNU126 to 0 turning off comms timeout trip
c) Make any changes to Parameter 121, $20 (Coil 974).
0 = 1 Stop bit
1 = 2 Stop bits
d) Store changes to eerom (save ram).
3) The 5MC standard keypad MUST BE DISCONNECTED while any optional
communication interface is fitted unless the interface provides a suitable connector. See the
relevant application note (APP00002) for connection of the various interface cards.
4) Details of registers and Flags are available in the FD8416 series of documents.
5) Register and coil addresses start at zero; register zero is addressed as zero, register
one is addressed as one …
Allowed address ranges are Register numbers 0…127, EEROM Registers 1000…1127,
Coils (flags) 0…1024.
6) Registers are mapped one to one, that is register one on the keypad is register one on
the Modbus.
7) Flags on the Modbus are read as holding registers i.e. read register 9 to read status2
flags. For writing flags are mapped one to one so for example the the Kick Start Flag bit 0 of
User Flags 1 (P51) is bit no 51 * 8 + 0 = Flag 408.