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16. Modicon PLC Programming Examples
This section of the manual is being provided solely as a brief overview of the
general ladder logic program architecture that can be used to interface with the
MBP-100 over a Modbus Plus network. For the most detailed information
available, the appropriate Modicon PLC Programming Manual should always be
consulted.
16.1 Ladder Logic and MSTR Instructions
Modicon PLCs that support Modbus Plus communications implement a special
instruction, called MSTR, which allows them to initiate Modbus Plus message
transactions via ladder logic. An example of a ladder logic program that
implements the MSTR instruction is shown in Figure 37.
MSTR on/off
Instruction End - Error
Instruction End - No Error
Instruction Completed
1
5
MSTR Instruction
40050
(Control Block)
40100
(Data Area)
100
(# data registers)
Instruction Active
2
3
4
5
3
4
Figure 37: Program Example for Modbus Plus Communications