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CMC TECHNICAL REFERENCE MANUAL
1X36003 Version 2.52
1996-1999 Ingersoll-Rand Company
Date of Issue: 18-Oct-1999
89
Example: Reading Multiple Coils
To read all sixteen digital (discrete) outputs, the following command is sent:
where relative address 00-BA is for digital (discrete) output for Channel 1. The response
from this command is:
To determine the state of each output, review the Electrical Schematic for your compressor.
For this example, you determine that the digital output for the prelube pump is located on
J12-P7,8 (Channel 13) and the digital output for the remote trouble contact is J15-P3,4
(Channel 3). The first hexadecimal data byte 04 (0000 0100 binary), represents the states of
the first eight digital (discrete) outputs (8-1). Therefore, for this example 04 means that
Channels 8, 7, 6, 5, 4, 2 and 1 are off and Channel 3 (compressor is in an alarm or trip
condition) is on. For the next eight channels (16-9) the hexadecimal data byte 10 (0001 0000
binary) means that Channels 16, 15, 14, 12, 11, 10 and 9 are off and Channel 13 (prelube
pump is running) is on. The following table graphically depicts this example:
A bit response of 1 means that the output is on and a response of 0 means that the output is
off.
Function 02 - Read Input Status
This function reads the state of one or more discrete inputs (MODBUS 1x references) in the
slave (CMC Base Control Module). For the CMC, these inputs represent the Discrete
(Digital) Inputs. If the function returns a 1, the input is on. If the function returns a 0, the input
is off. Broadcast is not supported. Refer to the table on the next page for MODBUS Absolute
Addresses for each discrete input supported by the CMC-MODBUS Interface.
Number of
Device
Function
Address
Coils
CRC
Address
Code
Hi
Lo
Hi
Lo
Lo
Hi
01
01
00
BA
00
10
1C
23
Device
Function
Byte
CRC
Address
Code
Count
Data
Lo
Hi
01
01
02
04-10
BA
F0
Response
8
7
6
5
4
3
2
1
Byte 1
0
0
0
0
0
1
0
0
Address
C1
C0
BF
BE
BD
BC
BB
BA
Response
16
15
14
13
12
11
10
9
Byte 2
0
0
0
1
0
0
0
0
Address
C9
C8
C7
C6
C5
C4
C3
C2