Rockwell Automation Publication 5069-UM003B-EN-P - January 2020 85
Compact 5000 I/O Serial Module Configuration Chapter 4
Master Command List Limitations
• A maximum of 50 commands can be created. The commands are subject
to available connection memory.
• Each Modbus Master supports up to two data connections.
• The First Data Connection supports a max of 464 bytes of read data and
476 bytes of write data. The Second Data Connection supports a max of
472 bytes of read data and 488 bytes of write data.
• Each command can have a max of either 125 words read or 123 words
write or 2000 coil/discrete input read or 1968 coils written.
• Each Read command uses:
– Four bytes of input data for command status
– Two bytes of input data per holding register or input register read.
– One byte of input data per every 1…8 coils or discrete inputs read.
– Padding to align command to 4 bytes.
• Each Write command uses:
– Four bytes of input data for command status
– Two bytes of output data per holding register written.
– One byte of output data per every 1…8 coils written.
– Padding to align command to 4 bytes.
• Remaining available data is displayed.
• An error message appears when connection memory is exceeded.
Master Command Memory Usage
Input and output data size is available in the Add-On Profile.
• View data size to verify data has not exceeded data available per channel:
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