User`s manual

MGate MB3000 User’s Manual Configuring the Modbus Gateway
9-16
Customize Modbus Settings
The Modbus tab is where certain adjustments can be made to fine tune the communication between
different Modbus networks. You can configure Initial Delay, Modbus TCP Exception, Slave
Channel, and Response Time-out.
Parameter Value
Initial Delay Numeric
Modbus TCP Exception Enable or Disable
Slave Channel Radio button
Response Time-out Numeric
Initial Delay
Some Modbus slaves may take more time to boot up than other devices. For certain environments,
this may cause the entire system to suffer from repeated exceptions during the initial boot-up. You
can force the MGate to wait after booting up before sending the first request with the “Initial
Delay” setting.
Modbus TCP Exception
The MGate MB3000 is a protocol gateway that transparently passes requests and responses between
the Ethernet and serial interfaces. In some situations, it may be necessary for the gateway to return an
exception in response to a request from a Modbus TCP master. This is enabled or disabled with the
“Modbus TCP Exception” setting. When enabled, the unit can return two types of exception:
Exception 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:
The request queue is full (32 request queue for each master)
The destination ID not included in the slave ID map.
Not all Modbus TCP masters require this exception, so it is up to you to determine if this setting
should be enabled.
Slave Channel and Response Timeout
According to the Modbus standard, the time that it takes for a slave device to respond to a request is
defined by the device manufacturer (please refer to Appendix A for details). Based on this response
time, a master can be configured to wait a certain amount of time for a slave’s response. If no
response is received within the specified time, the master will disregard the request and continue
operation. This allows the Modbus system to continue operation even if a slave device is
disconnected or faulty.
On the MGate MB3000, the “Response Time-out” field is used to configure how long the gateway
will wait for a response from a Modbus ASCII or RTU slave. This field is set independently for each
serial port, which is selected through the “Slave Channel” field. Please refer to your device
manufacturer’s documentation to manually set the response time-out.
The MGate MB3000 also provides automatic calibration of the response timeout. Instead of
manually figuring out the appropriate setting, you can click “Auto Detection” to have the MGate
figure out the setting for you. Once a value has been recommended, you can fine-tune it for best
performance.