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Modicon Communication Driver Manual
Modbus Plus Word and Bit References
The following section describes the use of Modbus Plus word and bit references in your configuration.
The general word referencing method is:
[plcname,word#format]
The “plcname” is the name of the designated PLC as listed in the PLC Name and Port Table. The
“word” is the reference number (address) of the word or register to be read or written. The “#format”
is a code that specifies the format of the data being read or written. The “plcname” and “#format” are
optional.
The general bit referencing method is:
[plcname,bit]
The “plcname” is the designated PLC as listed in the PLC Name and Port Table. The “bit” is the
reference number (address) of the bit, coil, or input to be written or read.
984-385, 984-485, 984-685, 984-785, Compact 984-145, 984-385E, 984-485E,
984-685E, 984-785E, and Quantum
The Modicon controllers listed above use decimal word addresses. The Operator Station format
default is BIN4. The following list contains the memory types supported by the Operator Station.
0XXXX
Coils/discrete
outputs
1XXXX
Discrete
inputs
(read
only)
3XXXX
Input
registers
(read
only)
4XXXX
Holding/output registers
900XX
Global data (Modicon Controllers; read only)
G00XX
Global data (Operator Station node)
An Operator Station with a Modbus Plus interface board cannot write to inputs, input registers, or
“900XX” global registers; therefore, control button bit references in the Operators Station editors refer
to Modicon coils (or holding/output registers for the 984-785 PLC).
Bit references in expressions refer to Modicon inputs or outputs.
All references to Controller words refer to Modicon registers.
Leading 0’s are not required unless specified.
The Modicon 984-X85 and Quantum controllers allow up to 100 contiguous words per single block
read. The maximum number of unused words is 98. If the Operator Station encounters 98 or more
unused words, then another block read is generated.
