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CMC TECHNICAL REFERENCE MANUAL
1X36003 Version 2.52
1996-1999 Ingersoll-Rand Company
Date of Issue: 18-Oct-1999
87
•
Absolute address for Coil 00127 decimal is relatively addressed as coil 007E hex (126
decimal)
•
Input register with absolute address of 30001 is relatively addressed as register 0000 in
the data address field of the message. The function code field that specifies reading or
writing data already specifies an input register operation; therefore, the 3x reference is
implicit.
•
Holding register with an absolute address of 40108 is relatively addressed as register
006B hex (107 decimal)
Single Module Addresses
The addresses provided in this document are for compressors with a single Base Control
Module.
Multiple Module Addresses
For those systems that require multiple Base Control Modules, the addresses for the first
module will be as provided within this document. The addresses for the second module will
be provided as an engineering submittal.
Data
For both queries and responses, the data is in sixteen bit (two bytes, one word) chunks. For
each two byte word, the left most byte is the most significant. For each byte, the left most bit
is the most significant.
This portion of the message changes with each function code. See the detail that follows for
each function for the specifics of this message component.
Byte Count
The number of bytes contained in the data portion of the message. This is used on both
queries (reads) and responses.
Cyclical Redundancy Check (CRC)
This portion of the message is used to prevent incorrect data from being used in the Master
or Slave because of communication errors.
Function Details
Function 01 - Read Coil Status
This function reads the state of one or more coils (MODBUS 0x references) in the slave
(CMC Base Control Module). For the CMC, these coils represent the Discrete (Digital)
Outputs, compressor operating state (see the Operator User Interface Status Bar for
definition), any compressor Trip condition and any compressor Alarm condition. If the
function returns a 1, the discrete output is on. If the function returns a 0, the discrete output
is off. Broadcast is not supported. Refer to the table on the next page for MODBUS Absolute
Addresses for each coil supported by the CMC-MODBUS Interface.