User Documentation
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Exception type: Conditions
Timeout There is no response from the slave. Maybe the device is off-line or the serial
cable is broken.
Request dropped There are two situations that will result in this exception:
1. The request queue is full (32 request queue for each master).
2. The destination ID not included in the slave ID map.
Note: Not all Modbus TCP masters require this exception. It depends on the application to determine if
this setting should be enabled.
Response Timeout (applicable to physical serial Port and virtual TCP/Procom ports)
According to the Modbus standard, the time that it takes for a slave device responding to a request is
defined by the device manufacturer. Based on this response time, a master can be configured to wait a
master will ignore the request and continue operation. This allows the Modbus system to continue
operation even if a slave device is disconnected or faulty.
On the Modbus Gateway the parameter Response Time-out is used to configure how long the
gateway will wait for a response from a Modbus ASCII or RTU slave. Please refer to your device
e time-out.
Button Auto Detection
The device also provides an automatic calibration of the response timeout. Instead of setting manually,
you can click button . The Modbus Gateway then starts a request for all defined slave
in menu item Slave ID. The response times will be displayed in a separate window.
Based on the results the timeout values can be set for best performance.
Inter-Character Timeout (Serial Port)
Use this function to determine the timeout interval between characters for Modbus devices that cannot
receive Rx signals within an expected time interval. If the response is timed out, all received data will
be discarded. Note that this timeout mechanism only works in RTU slave mode. The Modbus Gateway
automatically determines the timeout interval if the timeout value is set to 0.
Inter-Frame Delay
In operation mode RTU slave a user can determine the time-delay for transmitting the data frame
received from a slave device to the upstream. The device automatically determines the time-delay if it
is set to 0.