Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 44)

Publication 1757-UM006A-EN-P - May 2002
1-30 The Fieldbus Communication Model
through independent function blocks, so each require their own 40 to
50 milliseconds.
The 1788-CN2FF operates on the Fieldbus side at the max. speed of
the Fieldbus, and at the ControlNet rate on the ControlNet side.
Therefore, the 1788-CN2FF is not a limiting factor in a Fieldbus
systems performance. When a 1788-CN2FF operates, the Fieldbus side
and the CN side run asynchronously. When the CN2FF receives data,
it is stored in the CN2FF and is Produced on CN at the NUT rate.
Therefore, in a typical CN2FF Fieldbus system, the controller will be
receiving a lot of redundant data.
In a PLX system, with a FIM fieldbus interface, the Fieldbus side
operates at the Fieldbus data rate, and the controller side operates at
the backplane rate, so again, it is not a restriction on the performance
of a fieldbus system.