Cooper Bussmann VERSION 1.6 BU-945U-E 802.11 DSSS - Manual (Page 51)

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Cooper Bussmann Wireless Ethernet & Device Server BU-945U-E 802.11 DSSS User Manual
51 3A1582Rev1.6
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 Server 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 Server 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-945U-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 4.4 “Internal Diagnostic 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 (See 4.4 “Internal
Diagnostic 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.