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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
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middle of the loop that may have the wires reversed, or shorted together. Check the Modbus faq on the obvius.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 AcquiSuite
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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
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possible, bring the failed device adjacent to the AcquiSuite and attach it with a short stub of wire to eliminate possible
wiring problems. If the AcquiSuite 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 AcquiSuite. Usually, the AcquiSuite will locate the device and
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print "Unknown" in the device status column if the device is not recognized by the AcquiSuite 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 AcquiSuite firmware version. If not, check for firmware upgrades online with the
Firmware Update configuration page.
Remember, the AcquiSuite may take between 2 and 5 minutes to detect a new device that has been attached to the
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Modbus rs485 loop. Rebooting the AcquiSuite, 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.
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Modbus Setup
The Modbus setup page provides several options related to the Modbus RS485 serial port.
AcquiSuite Name: This is the name of the AcquiSuite. 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 AcquiSuite 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 AcquiSuite. Options range from once per minute to once per
hour. All of the selections are even divisions of one hour. The AcquiSuite 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 AcquiSuite 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
AcquiSuite to gather information for meters that require demand calculations, as well as provide accurate information
starting when the AcquiSuite is booted.
Modbus/TCP access: The AcquiSuite 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 password or other methods of security. By default, the gateway feature is disabled, and set to "No
Access."
The Modbus TCP gateway is a feature that allows the AcquiSuite to share the attached Modbus RS485 devices with other
systems such as PCs with software and building control systems. The gateway receives incoming TCP requests, verifies the
length of the packet does not exceed 255 bytes, and forwards the packet to the Modbus RS485 loop. The gateway does not
verify the contents of the packet, nor the target address specified in the request. If the Modbus RS485 device sends a valid
response back, the gateway will return this information to the the system requesting it via TCP. If no response is received, a
timeout failure will be sent to the requester. Because the gateway does not process the contents of the request or reply, it is
possible to query devices on the Modbus RS485 loop that are not specifically supported by the AcquiSuite. A Modbus/TCP
technical guide may be available soon.
Modbus RS/485 baud rate: This feature allows the configuration of the RS485 serial port speed which the AcquiSuite uses
to communicate with Modbus devices. Options include 9600, 19200, 38400, 57600, and 115200. The default is 9600, most
Modbus devices communicate at this speed as well. Multiple baud rates may be selected in this menu. If multiple rates are
selected, the AcquiSuite will automatically detect the baud rate of each Modbus device from the chosen options. Once the
baud rate has been detected for a specific Modbus device address, and will continue to communicate with that specific
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Table of Contents
Troubleshooting
