Rockwell Automation 1756-DHRIO_DHRIOXT ControlLogix Data Highway Plus-Remote I/O Communication Interface Module - Manual (Page 166)

166 Rockwell Automation Publication 1756-UM514C-EN-P - June 2014
Appendix B Application Guidelines and Tips
RPI Formula without Block
Transfer Modules Digital Modules
This formula is for a worst case scenario with only discrete modules.
• Scan Rate =
–
3ms/adapter for 230.4K Baud
– 5ms/adapter for 115.2K Baud
– 8ms/adapter for 57.6K Baud
• Link Time = scan rate * (# of adapters)
• Recommended RPI = 0.5 * link time
• Maximum Update Time = RPI + 2 * (link time)
Worst Case Scenario
This formula is for a worst case scenario.
• Scan Rate =
–
3ms/adapter for 230.4K Baud
– 5ms/adapter for 115.2K Baud
– 8ms/adapter for 57.6K Baud
• Link time = scan rate * (# of adapters + # of adapters with block transfer
modules)
• Recommended RPI = 0.5 * link time
• Maximum Update Time = RPI + 2 * (link time)
Increase the Unconnected
Message Buffer Limit You can find more information on increasing the unconnected message buffer
limit at the Rockwell Automation knowledge base at:
https://rockwellautomation.custhelp.com/
• With RSLogix 5000 version 8.02 the Unconnected Message Buffer can be
increased from the default value of 10 to a total of 40 with a CIP Generic
Message instruction.
• A penalty of 1K of I/O memory is consumed for each increase above 10
• A source and destination array must be configured. Each needs to be
configured as SINT type with 30 arrays.
• The communication path is set to: 1, slot number of the controller.
• The CIP Generic message has to be enabled once, after that another CIP
Generic message must be used to change the value.