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245U-E Wireless Ethernet Modem User Manual
57
Rev Version 2.24
Enable Modbus
Statistics
Enables the Modbus diagnostic registers, as shown in “4.9 Internal Diagnostics
Modbus Registers.” Disabling this option will free up the registers and also
slightly increase processing resources.
Log background Noise
RSSI and BGND on RX messages are made available in the diagnostic registers
See “4.9 Internal Diagnostics Modbus Registers” for details. For a hexadecimal
value of 5F5D, the 5D byte = RSSI and the 5F byte = BGND. Convert the value
from hexadecimal to decimal and add a “-” (for example, 5F = -95dB). Disabling
this option removes the background noise byte from these registers so that
only the RSSI value is made available.
Modbus TCP Client Mappings on I/O Transfer Menu
Local Register
Enter the starting onboard I/O register number that the specified Modbus
master transaction will transfer I/O to/from.
I/O Count
Specify the number of consecutive I/O register to be transferred for the
specified transaction.
Function Code
Specify the Modbus function code for the transaction.
Destination Register
Enter the starting I/O register number in the destination device that the
specified Modbus master transaction will transfer I/O to/from.
Device ID
Enter the Modbus device ID of the destination Modbus device
Server IP Address
Specify the IP address of the destination Modbus TCP server for the specified
transaction.
Response Timeout
Enter the timeout (in milliseconds) to wait for a response to the specified
transaction.
Comm Fail Register
Enter the onboard I/O register number to store the communication
status of the specified transaction. The specified register will be set to 0 if
communications is successful, 0xFFFF if there is no connection to the specified
server, or 0xFFxx where “xx” is the Modbus exception code
3.16 Roaming
In certain cases a client may be in a mobile situation and require a method of roaming to another access
point. Normal network communications provide only basic roaming behavior, which means as the client
moves further from the access point it will go through a period of poor communication followed by a
complete disconnection of the radio link. It is at this point that the client will scan for access points, and if
one is in range it could take up to 10 seconds for the client to establish a connection.
Fast roaming will significantly reduce the time taken for a client to roam from access point to access point.
In addition, the discovery of access points is completed before the existing radio link deteriorates, therefore
eliminating the periods of poor performance during transition to the next access point.