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MVI56-MCM ♦ ControlLogix Platform Reference
Modbus Communication Module
Page 100 of 159 ProSoft Technology, Inc.
July 24, 2008
The ladder logic will be responsible for parsing and copying the received
message and performing the proper control operation as expected by the master
device. The processor must then respond to the pass-through control block with
a write block with the following format.
Offset Description Length
0 9958 1
1 to 247 Spare 247
This will inform the module that the command has been processed and can be
cleared from the pass-through queue.
Function 6 and 16
Offset Description Length
0 0 1
1 9956/9957 (Floating-point) 1
2 Number of data words 1
3 Data Address 1
4 to 248 Data 244
249 9956/9957 1
The ladder logic will be responsible for parsing and copying the received
message and performing the proper control operation as expected by the master
device. The processor must then respond to the pass-through control block with
a write block with the following format.
Offset Description Length
0 9956/9957 1
1 to 247 Spare 247
This will inform the module that the command has been processed and can be
cleared from the pass-through queue.
Function 15
When the module receives a function code 15 when in pass-through mode, the
module will write the data using block ID 9959 for multiple-bit data. First the bit
mask clears the bits to be updated. This is accomplished by ANDing the inverted
mask with the existing data. Next the new data ANDed with the mask is ORed
with the existing data. This protects the other bits in the INT registers from being
affected.
Offset Description Length
0 0 1
1 9959 1
2 Number of Words 1
3 Word Address 1
4 to 53 Data 50
54 to 103 Mask 50
104 to 248 Spare 145
249 9959 1