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8 MODBUS
8.7 Troubleshooting Pulse Inputs
If the device you have attached does not appear in the Modbus device list, check the following:
•
Verify the pulse input connections are correct.
•
Verify the status LED blinks for the specific pulse input in question. Try bridging the two terminals at the
input of the EMB HubLite to verify the input LED turns on.
•
Bridge the terminals of the pulse output meter and verify the input LED turns on. This will verify the
wiring to the meter is correct.
8.8 Modbus Setup
The Modbus setup page provides several options related to the Modbus RS485 serial port.
EMB HubLite Name:
This is the name of the EMB HubLite. 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
EMB HubLite 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 EMB HubLite . Options range from once per
minute to once per hour. All of the selections are even divisions of one hour. The EMB HubLite 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 EMB HubLite 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 EMB HubLite to gather information for meters that require demand
calculations, as well as provide accurate information starting when the EMB HubLite is booted.
Modbus/TCP access:
The EMB HubLite has a Modbus/TCP gateway feature that allows other syste ms
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 EMB HubLite 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 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
EMB HubLite. A Modbus/TCP technical guide may be available soon at www.leviton.com.
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