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8 MODBUS
8.7 Troubleshooting Modbus Devices
If the device you have attached does not appear in the Modbus device list, check the following:
•
Verify the + (red), - (black), and Shield connections are correct on all connections. Look for any
connection in the middle of the loop that may have the wires reversed, or shorted together. Check the
Modbus FAQs on the leviton.com website for further details on wiring a Modbus serial connection.
•
Verify the address settings of every Modbus device. No two devices may have the same address.
Note: the Energy Monitoring Hub A8812 uses the address 250 for the internal IO module. Do not assign
this address to any other Modbus device.
•
If only one device is not working, try disconnecting all the other devices on the Modbus loop to isolate
the problem. If possible, bring the failed device adjacent to the DAS and attach it with a short stub of
wire to eliminate possible wiring problems. If the DAS can find a device on the short stub, the problem is
probably a wiring related issue on the RS485 loop.
•
Check to verify the Modbus device is supported by the DAS . Usually, the DAS will locate the device and
print “Unknown” in the device status column if the device is not recognized by the DAS firmware drivers.
In the lower right corner of this screen, there is a link that will show a list of supported devices. Use
this to verify the Modbus device in question is supported by the DAS firmware version. If not, check for
firmware upgrades online with the Firmware Update configuration page.
•
Remember, the DAS may take between 2 and 5 minutes to detect a new device that has been attached
to the Modbus RS485 loop. Rebooting the DAS, refreshing the device list page, or using the console
“Modbus status” menu will not speed up the recognition process.
• Click the “Troubleshooting” link at the bottom of the Modbus device list page for further diagnostics.
8.8 Modbus Setup
The Modbus setup page provides several options related to the Modbus RS485 serial port.
DAS Name
: This is the name of the DAS. This name will be present on all log file descriptors when
uploaded to a central database website such as BMO. It is helpful to name the DAS based on the physical
location of the system, or building. Note: this feature was labeled “Loop Name” in older firmware versions.
Data logging period:
This option sets the log interval for the DAS. Options range from once per minute
to once per hour. All of the selections are even divisions of one hour. The DAS calculates the next log
time by finding the next multiple of the log period past the start of the hour. For example, if the log period
is 15 minutes, log readings will be taken at 0, 15, 30 and 45 minutes past the hour. The log period is not
calculated based on “15 minutes after the last reading”.
When the DAS is first started, it will take an initial reading of all the Modbus devices immediately. Following
that, the next log reading will be calculated as a multiple of the log period after the hour. The initial reading
is taken to allow the DAS to gather information for meters that require demand calculations, as well as
provide accurate information starting when the DAS is booted.
Modbus/TCP access:
The DAS has a Modbus TCP gateway feature that allows other systems to send
queries to all attached Modbus RS485 devices. This feature allows control of what systems have access
to the Modbus TCP gateway feature. The settings include “no access”, “local subnet only” and “allow any”.
This basic security feature only allows control based on the IP address of the system making the request.
The Modbus TCP protocol does not have provisions for any authentication passw ord or other methods of
security. By default, the gateway feature is disabled, and set to “No Access.”.
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