A Profibus data module term


Thread Starter

Joe O

I am somewhat new to Profibus and I find it relatively easy to configure. However, I do have a question regarding a term used in the data module set-up.
What is the difference between “consistent” and “non-consistent” data modules?


Peter Nachtwey

Consistent data is sent as one block data so it sent at the same time or scan and received at the same time or scan as one block of data. Non-consistent data my be from two scans so no relation ship between bytes or words can be assume. This is ok for discrete I/O butnot for analog or counter values.

A sixteen bit counter would not be very useful if the high byte changed one PLC scan and the low byte changed the next plc scan. Both bytes must be changed togeather. Likewise for more intelligent modules where multiple registers are required such as a motion controller.