Leviton A8810, Инструкция по установке и эксплуатации, Страница: 23 / 44

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8 MODBUS
The Modbus TCP gateway is a feature that allows the EMB Hub 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
add ress 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
EMB Hub. A Modbus/TCP technical guide may be available soon at www.leviton.com.
Modbus RS/485 baud rate : This feature allows the configuration of the RS485 serial port speed which the
EMB Hub 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 EMB Hub 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 device address at the detected
speed. This feature will allow you to mix multiple devices on the same RS485 loop with different baud
rates. Modbus devices default to a baud rate of 9600. Note: Modbus device manufacturers usually do not
‘officially’ support this configuration, however we have not seen any problems with this in any of the Modbus
devices we provide drivers for. Most Modbus devices simply ignore packets received at the wrong baud
rate. If you are experiencing Modbus communications problems, you should set the baud rate to a fixed
9600 before troubleshooting.
Modbus RS485 Parity: This feature allows alternate parity options to be set. Default is no parity.
Modbus RS485 Stopbit: This feature allows alternate stop bit options to be set. Default is one stop bit.
Modbus RS485 timeout: This feature sets the period of time the EMB Hub will wait for a response from
any device on the Modbus RS485 serial loop. The default of 200ms is long enough for most Modbus
devices. Longer timeouts may be required if you have a very slow device, or if you have a Modbus repeater
device in the serial loop. Devices such as the ModHopper, the Veris H8936 Local Display, or any RS485
wireless link repeaters add a substantial delay. Setting the delay longer than the default will increase the
time required to auto detect new Modbus devices when attached to the EMB Hub. For ModHopper con
nections, use a minimum setting of 1.5 seconds. The allowed range is 100ms to 5 seconds.
Tip: Set the timeout to the longest available setting, and use the “stats” option on the bottom right of the
device list page to monitor the actual RTT (response time) for each device. Next, decrease the RS485
Timeout that is close to (but longer than) the slowest device in the device list.
Modbus RS485 Debug: This feature records Modbus RS485 transaction data in the system debug log file.
You must click the “start log” button on the system/log files page to record this information. Debug options
are as follows:
•
None: No RS485 information is logged.
• Errors: Only Modbus errors are logged.
• Transaction: One line is logged describing every RS485 query, and the result of that query.
• Full Debug: Complete listing of all queries including hex dumps of all data sent/received.
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