System Monitor
Message
Function Code
Read Input Status
2
Read Input Register
4
Loopback/Maintenance
8
Report Slave ID
17
16
PROTOCOL SPECIFICATIONS
MODBUS PROTOCOL MESSAGE TYPES
A Serial Interface in a Modbus protocol connection will behave as a slave only. The mode of
transmission is RTU. The messages that will be allowed to be received and transmitted by the
Serial Interface are as follows:
Note
All input point and input register addresses referenced in this document are zero
based. Modicon programmable controller (PC) locations are one based. The
address references in this manual relate directly to the modbus message format.
If local host programming uses Modicon PC addresses the appropriate base
conversion from one to zero must be kept in mind. For example: Input point
address 0 = Modicon PC point 10001; Input register address 0 = Modicon PC
register 30001. Refer to the Modicon Modbus protocol document listed in the
forward for a complete review of Modicon PC formats.
READ INPUT STATUS
This command reads monitor status values from the interface.
READ INPUT REGISTER
This command reads monitor direct values from the interface.
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Summary of Contents for 3300/01 Series
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