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8 MODBUS
8.2 Device List Options
At the top of the Modbus device list page, there are several display options that control the sorting of the
device list.
Tree display: click this icon to organize the list by showing each ModHopper
®
, and the devices
attached to each one.
List display: (default) show the list of Modbus devices sorted by the Modbus address number.
At the bottom of the Modbus device list, there are several options that may be selected to view or configure
all the Modbus devices at the same time. These options are as follows:
Add:
Manually add a Modbus device to the device list. This option can be used to configure a Modbus
device that is not presently connected to the system, add a framework configured device, or add a Modbus/
TCP connected device. See the section on manually adding a device below.
Troubleshoot:
The DAS will review the devices connected and offer suggestions about any problems found.
Rename all devices:
This option allows you to edit all the device names in one configuration page.
This is useful when initially configuring a large number of new devices. A name must be assigned to a
device before the DAS will log data for it.
List all supported devices:
This option will show a list of all Modbus devices with built in drivers in the
installed firmware.
Show [setup]:
Display links for Device configuration and Advanced configuration for each device.
Show [devinfo]:
Display the communications options including baud rate, serial number and firmware
version (when available) for all devices in the Modbus device list.
Show [stats]:
show packet counters for all devices in the device list. These include
Sent
: Total number of packets sent to this Modbus
Received:
Total number of valid packets received from this Modbus address.
Error:
Total number of packets received that fail CRC for this device. (does not include non
response queries)
RTT:
The average round trip time for the last 7-10 packets that received a valid response. This value
is useful in configuring the Modbus timeout in the ModbusSetup/RS485 page. Note: if the timeout is
set too short, you will not see an accurate value because packets dropped for timeout are not counted
for RTT.
XML:
Display the device list data in XML
Notes on RTT and Timeout configuration:
To best measure the true RTT, set the ModbusSetup/RS485 timeout to the maximum period and allow the
DAS to run for 5 or 10 minutes. Next, review the RTT values seen in the device list page and make note of
the longest RTT time shown for any device. Last, configure the ModbusSet up/RS485 timeout to the option
that is the next largest than the longest time seen for any device. For example if the worst RTT is 600ms,
set the timeout to 1 second.
Typical RTT values for direct connected devices should range between 40ms and 200ms. Systems that
have wireless links such as ModHoppers should expect an additional delay of 500ms per hop. A complex
system with multiple ModHoppers may have RTT values upwards of 3 seconds.
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