ProSoft Technology 5202-DFNT-MCM4 - Manual (Page 54)

MCM ♦ ProLinx Gateway Modbus Port Expander (4102/5102-MBS3-MBM)
Modbus Master/Slave Driver Manual
Page 54 of 80
ProSoft Technology, Inc.
October 16, 2009
7.2.11 Use CTS Line
Y ES or N O
This parameter specifies if the Clear To Send (CTS) modem control line is to be
used or not. If the parameter is set to N
O , the CTS line will not be monitored. If
the parameter is set to Y ES , the CTS line will be monitored and must be high
before the gateway will send data. Normally, this parameter is required when
half-duplex modems are used for communication (2-wire). This procedure is
commonly referred to as hardware handshaking.
7.2.12 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.