ProSoft Technology MVI46-MCM - Manual (Page 23)

MVI46-MCM ♦ SLC Platform Configuring the MVI46-MCM Module
Modbus Communication Module User Manual
ProSoft Technology, Inc. Page 23 of 108
March 29, 2011
File M0 Offset Register Content Description
N10:62 63 5062 Response
Timeout This parameter represents the message response
timeout period in 1 ms increments. This is the time that
a port configured as a master will wait before re-
transmitting a command if no response is received from
the addressed slave. The value is set depending on to
communication network used and the expected
response time of the slowest device on the network.
N10:63 64 5063 Retry Count This parameter specifies the number of times a
command will be retried if it fails. Enter a value in the
range of 0 to 10.
N10:64 65 5064 Error Delay Count This parameter specifies the number of polls to be
skipped on the slave before trying to re-establish
communications. After the slave fails to respond, the
master will skip commands to be sent to the slave the
number of times entered in the parameter. Enter a
value in the range of 0 to 65535.
N10:65 66 5065 Reserved
N10:66 67 5066 Use Guard Band
Timer Use packet gap timeout for messages (Yes or No). Use
only in multi-drop applications.
N10:67 68 5067 Guard Band
Timeout
A value of 0 uses the default baud rate or you can set a
timeout value in milliseconds (0 to 65535).
N10:68 69 5068 Spare
N10:69 70 5069 Spare
Guard Band parameters
With multiple nodes in the network (multidrop), the module must be able to define
the time period used to properly recognize the received data sequence as a valid
Modbus message. This time period is defined through the guardband timer
parameter. Failure to set the Guard Band functionality may cause successive
communication errors in the Modbus network.
This functionality is only used for Modbus RTU mode, when the module is
configured as a slave device in a multidrop network (RS-422 or RS-485 wiring).
In RTU mode, when the module receives sequence of data from another node, it
will recognize the end of the message when it detects a 3.5 character gap. The
next byte received after a 3.5 character gap will be recognized as the start of a
new Modbus message.
The 3.5 character gap depends on the port communication settings, especially
the baud rate. The higher the baud rate, the lower the corresponding time period
equivalent to the 3.5 character delay.