ProSoft Technology 5202-DFNT-MCM4 - Manual (Page 24)

MCM ♦ ProLinx Gateway MCM Protocol Configuration
Modbus Master/Slave Driver Manual
Page 24 of 80
ProSoft Technology, Inc.
October 16, 2009
3.1.22 Holding Register Offset
0 TO 3999
When the port is configured as a slave, this parameter specifies the internal
database address to use as the zero address or starting point for Holding
Register (16-bit integer) data. Holding Register data is read by Modbus Function
Code 3 commands (Read Holding Registers) and written by Function Code 6
(Preset Single Register) or Function Code 16 (Preset Multiple Registers).
For example, if this parameter is set to 1000 and a Function Code 3 command is
received requesting Holding Register address 0 (virtual Modbus address 40001
or 400001), the data returned in the response will be the value at register 1000 in
the gateway's database.
3.1.23 Use Guard Band Timer
Y ES or N O
This parameter specifies if the Guard Band feature (intercharacter delay
monitoring and control) is to be used or not. Normally, this feature will not be
needed. It is used only when the port is set for Modbus RTU mode as a slave
device in a multi-drop, multi-node network (RS-422 or RS-485 wiring). If the
remote Master experiences multiple, successive failures when trying to
communicate with the gateway on a multi-drop network, setting a small amount
of Guard Band Time will usually completely eliminate the failures.
When the port is configured as a slave and when multiple slave nodes exist on
the network (multi-drop), without the Guard Band Timer, the gateway might not
be able to properly discriminate between a response message returned by
another slave and a command from the Master to which it should respond. The
Guard Band Timeout parameter allows you to set a small delay which can help
eliminate communication errors on the Modbus network.
To enable the Guard Band Timeout parameter:
1 First of all, enable the the Use Guard Band Timer parameter.
Use Guard Band Timer = Y
2 Then, set the Guard Band Timeout.
Guard Band Timeout = 0
This configuration will set the gateway to use a pre-defined time interval for
Modbus message recognition calculated for each baud rate. This should
provide optimal performance for most applications.
If you still observe a considerable number of communication errors, try to
increase the Guard Band Timeout value until the network performance is
improved.