Supported Data Packet Size For Cip Serial Function - Allen-Bradley Micro800 General Instructions Manual

Chapter 9
Communication instructions
196

Supported Data Packet Size for CIP Serial Function

For Micro830 and Micro850 controllers, both embedded serial port and plug-in
serial ports can support CIP serial communication. CIP serial communication
data packet includes user data and CIP packet header.
When working as a CIP serial client, Micro830/Micro850 serial ports can support
a maximum of 490 bytes of read/write user data. This maximum specification
applies to CIP serial data packets with a minimum packet header size. When the
size of a packet header is bigger than the minimum packet header size, the
maximum size of user data that the CIP client can support is less than 490 bytes. If
data packet size is greater than the maximum data size supported by the CIP
client, the function block reports an error (0x21) and a sub-error (0x33).
When working as a CIP serial server, Micro830/Micro850 serial ports can support
a minimum of 255 bytes of read/write user data. This minimum user data size
specification applies to CIP serial data packets with maximum packet header size.
When the size of CIP packet header is less than the maximum packet header size,
the CIP client can support data packet size that is greater than the minimum
specification (that is, greater than 255 bytes). However, if user data size is greater
than the maximum data size supported by the CIP server function, the CIP data
packet could be dropped, and the client will time out.
Important: For CIP serial server function, it is recommended not to read/write more than 255 bytes of user data in a single CIP
message.
Rockwell Automation Publication 2080-RM001D-EN-E - February 2015