Publication 1756-UM514B-EN-P - February 2003
C-4 Application Guidelines and Tips
RPI Formula without Block
Transfer Modules
Digital Modules Only
This formula is for a worst case scenario with discrete modules only.
· 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)
Increasing the
Unconnected Message
Buffer Limit
In addition to below, you can find more information on increasing the
unconnected message buffer limit at the Rockwell Automation
knowledge base at: http//support.rockwellautomation.com.
· With RSLogix5000 version 8.02 the Unconnected Message Buffer
can be increased from the default value of 10 up to 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 set up as SINT type with 30 arrays.
· The communication path should be 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.
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