MBS Protocol
PLX3x Series ♦ Multi-Protocol Gateways
User Manual
Page 126 of 215
ProSoft Technology, Inc.
January 25, 2018
Parameter
Value
Description
MB Address
in Device
Varies
Specifies the starting Modbus register or bit address in the server for the
command. Refer to the documentation of each Modbus server device for
the register and bit address assignments valid for that device.
The
Modbus Function
code determines whether the address is a
register-level or bit-level OFFSET address into a given data type range.
The offset is the target data address in the server minus the base
address for that data type. Base addresses for the different data types
are:
00001 or 000001 (0x0001) for bit-level Coil data (Function Codes 1,
5, and 15).
10001 or 100001 (1x0001) for bit-level Input Status data (Function
Code 2)
30001 or 300001 (3x0001) for Input Register data (Function Code
4)
40001 or 400001 (4x0001) for Holding Register data (Function
Codes 3, 6, and 16).
Address calculation examples:
For bit-level Coil commands (FC 1, 5, or 15) to read or write a Coil
0X address 00001, specify a value of 0 (00001 - 00001 = 0).
For Coil address 00115, specify 114
(00115 - 00001 = 114)
For register read or write commands (FC 3, 6, or 16) 4X range, for
40001, specify a value of 0
(40001 - 40001 = 0).
For 01101, 11101, 31101 or 41101, specify a value of 1100.
(01101 - 00001 = 1100)
(11101 -10001 = 1100)
(31101 - 30001 = 1100)
(41101 - 40001 = 1100)
Note:
If the documentation for a particular Modbus server device lists
data addresses in hexadecimal (base16) notation, you must convert the
hexadecimal value to a decimal value for this parameter. In such cases,
you usually do not have to subtract 1 from the converted decimal
number, as this addressing scheme typically uses the exact offset
address expressed as a hexadecimal number.
