MODBUS-GW Installation and Operation Manual —
P/N LS10015-000NF-E:C2 4/30/2019
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Section 6 Troubleshooting
6.1 What are some basic guidelines I should use when installing a MODBUS-GW?
• Polling should be done slowly to start.
• Use Modscan
®
to debug the system rather than a more complicated client. Verify that registers are being updated as events
happen on the NFN network/panel.
• Make sure gateway can be pinged from the same computer on which the client application is being installed.
• Check and double check the power supplies as well as all cabling.
• Make sure the client supports Unit IDs.
• Stop the client from sending a subsequent request until after it receives a response from the gateway.
• Make sure the client accepts all exception responses. Including 0xA and 0xB.
• Use Wireshark
®
to debug IP traffic.
• Be sure only one client is polling the gateway.
• Check the MODBUS-GW configuration tool and be sure that the Authorized Client IP address is set to
0.0.0.0
. If using the
Authorized Client IP security feature, confirm that the address in the gateway matches the address in the Modbus client.
6.2 How fast can the Modbus client poll the gateway?
The polling rate is a function of several variables. Some issues that will determine the maximum poll rate are:
• The size of the NFN network that is being monitored.
• The number of points on the panels.
• The event activity on the NFN network/panel (i.e. VeriFire downloads).
• Requests for analog values are much slower than other requests
• If only a partial response form the gateway is seen in the Modbus client, try increasing the “response time out” value in the client
to a larger value. If the value is set to 5 seconds or more, this should be adequate. The exact response time out will depend on IP
network delays and routing. On a small IP network, the gateway responds to a read of 100 register in less than 1 second.
The gateway also has some processing overhead in order to do such things as maintain the registers.
6.3 How can I tell if the gateway is running?
• Ping the gateway from the computer on which the Modbus client is running.
• Use Wireshark to analyze the data on the IP network.
• Modscan was one tool that was used during development to test the gateway. It is designed primarily as a testing device for
verification of correct protocol operation in new or existing systems.
6.4 How do I recover a lost password from the gateway?
If the password for the gateway is lost, programming changes cannot be made. In this situation, the gateway settings must be reset. Refer
to
Appendix A, “Gateway Settings”
for instructions.
6.5 What is an “initialization read” for analog values?
This is the first read of up to 10 analog values from a 4–20 mA module. This first read tells the gateway that it should begin a polling
routine for the analog values in this request. The first response from the initialization will usually be all zeros. Subsequent responses will
have the actual values.
6.6 How many analog values can I read at a time?
Ten analog values can be read at one time. An initialization read must be performed.
6.7 Why do I get an exception code when trying to read an analog value?
There are several reasons why an exception code is received when requesting an analog value:
• The point from which an analog value is being requested is not a 4–20 mA analog input module.
• At least one of the points in the group of points from which an analog value is being requested is not a 4–20 mA analog input
module.
• More than 10 analog values have been requested in a single request.
6.8 Why do I get all zeros when I read an analog value?
There are several reasons a zero reading from an FMM-4-20 Analog Input Module is received:
• The first read for an analog value from the gateway initializes the polling routine in the gateway to retrieve analog values from
the NFN network. The first response will usually be all zeros. This is normal. The subsequent polls of an analog value for the
same point or group of points will return actual values. As long as the same points continue to be polled at a rate faster than the
Analog Poll Time Out, then the gateway will continue to poll the same points.
• The gateway does not actually take an analog value reading unless the module has reached the first threshold and therefore it will
return a zero reading.
• If the client polls the gateway too quickly after the initialization poll then the gateway may still return zeros.
• If the client polls the analog values slower than the Analog Poll Time Out, then the gateway may return all zeros.