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Cooper Bussmann BU-245U-E Wireless Ethernet & Device Server User Manual
• The first will write the register 4300 (Local Digital Input) to server IP address 192.168.0.200 (Unit B), Device ID #1, register 4320
(Local Digital output).
• The second mapping shows a Modbus read command of 8 Discretes starting at register 1 (Destination Reg) on Device ID #6 connected to IP
address 192.168.0.123 (it self) and store the values at register #1 locally.
�� The third mapping shows the Modbus write command (Write Coils) which is writing the local 8 I/O’s starting at register 1 across to Server IP
address 192.168.0.200, Device ID #5,destination reg #1.
The configuration of unit B is shown below (accessible via the “I/O Transfer”configuration page). It can be seen that Modbus TCP Client has been
enabled with a 500msec scan rate, meaning that there will be a 500msec delay between each of the mappings directed at any server.The “Reset
Registers on Comms Fail” option is enabled with a timeout of 60 seconds,indicating that any of the registers at unit B will be reset if a successful
Modbus transaction involving that register has not been executed in the last 60 seconds.The Modbus TCP to RTU Gateway at B must also be
enabled (see section “3.13.3 Modbus TCP to RTU Gateway”) to allow Modbus communications with the serial device A.
Three “Modbus TCP Client Mappings”are also configured at B in order to perform the required I/O transfer. The first mapping transfers the status
of the onboard digital input at C to the onboard digital output at B. Local Register 4320 specifies the register for the onboard digital output at B
(since B is the local unit at which the mapping is configured). I/O Count 1 specifies that only one I/O point is being transferred (i.e.,the single
digital I/O). Function Code 02:Read Discretes specifies the standard Modbus function code to read discrete (i.e., digital) inputs. Destination
Register 4300 specifies the register for the onboard digital input at unit C (since C is the destination unit for this mapping). Device ID 1is the ID of
the onboard Modbus TCP Server at C. Server IP Address 192.168.0.200 is the IP address of unit C – which is the Modbus TCP Server we are
reading from. Response Timeout 1000 ms specifies that unit C must respond to this message within 1000ms.Comm Fail Register 0 specifies the
local register where the communications status for this mapping will be stored.
The second mapping reads 8 registers from serial unit D into onboard registers in unit B. Note that in this case the specified Device ID 6 is the
Modbus Address of the serial device D,while the Ser ver IP Address 192.168.0.200 is the IP Address of unit C since the Modbus TCP to RTU
Gateway at unit C converts the Modbus TCP message to Modbus RTU and routes it out the serial port to unit D.
The third mapping takes the 8 registers read by the second mapping and writes them to the serial unit A.The specified Device ID 5 is the Modbus
Address of the serial device A,and the Ser ver IP Address 192.168.0.196 is the IP Address of the local unit B since the local Modbus TCP to RTU
Gateway is to route the message out the serial port to unit A.
Since the BU-245U-E supports Modbus TCP Client and Server simultaneously,the Modbus TCP Server for unit B above could also be enabled.
This would allow one (or more) external Modbus TCP Clients anywhere on the extended wired or wireless network to connect to unit B and
monitor the status of the I/O registers – including the I/O at units A,C, and D. This is a very powerful and flexible feature which could, for
example, be exploited by a central monitoring facility or SCADA.
Modbus TCP Configuration on I/O Transfer Menu:
Enable Modbus TCP Server (Slave) Check this box to enable the onboard Modbus TCP Server. All Modbus TCP connections to the module
IP Address and specified Modbus Server Device ID will be routed to the onboard I/O registers.
Modbus Server Device ID Specify the Modbus Device ID for the onboard Modbus TCP Server. Allowed values are 0 to 255.
Enable Modbus TCP Client (Master) Check this box to enable the onboard Modbus TCP Client.I/O to be transferred via the Modbus TCP
client is specified with Modbus TCP Client Mappings.
Modbus Client Scan Rate Enter the delay (in milliseconds) between execution of consecutive Modbus TCP Client Mappings to the
same Server.
Reset Registers on Comm’s Fail When Enabled the value in any onboard I/O register will be reset to zero if a valid Modbus transaction
directed to/from the given register has not been completed for longer than the Comms Fail Timeout.
Comms Fail Timeout The period of time after which onboard I/O registers will be reset if a valid Modbus transaction directed
at that register has not completed.
Enable Modbus Statistics Enables the Modbus Diagnostic registers as shown in Section 4.5 “Internal Diagnostics Modbus
Registers” Disabling this option will free up the registers and also slightly increase processing resources.
Log background Noise RSSI & BGND on Rx messages are made available in the diagnostic registers (Section 4.5 “Internal
Diagnostics Modbus Registers” for details.For a Hex value of 5F5D the 5D byte = RSSI and the 5F
byte = BGND (Convert value from hex to dec and add a “-“e.g.5F = -95dB). Enabling this option
removes the RSSI byte from these registers and so only the Background Noise value is made available.
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