![Knick Protos COMFF 3400-085 User Manual Download Page 9](http://html.mh-extra.com/html/knick/protos-comff-3400-085/protos-comff-3400-085_user-manual_1980137009.webp)
9
Foundation Fieldbus (FF) Technology
Bus Communication
Foundation Fieldbus (FF) permits cyclic and acyclic services:
•
Cyclic Services - Scheduled Communication:
are used for transmission of measurement data with status information.
The Link Active Scheduler maintains a list of transmission times for all data
in all devices that need to be cyclically transmitted. When it is time to trans-
mit data, the LAS issues a “Compel Data (CD)” start signal to the respective
device. Upon receipt of the “Compel Data” signal, the device broadcasts the
data to all devices on the fieldbus.
• Acyclic Services - Unscheduled Communication:
are used for device configuration, remote maintenance and diagnostics
during operation.
All devices are given the chance to send acyclic (unscheduled) messages
between transmissions of cyclic (scheduled) data. The LAS grants permis-
sion to a device to broadcast acyclic messages by issuing a “Pass Token
(PT)” message. Upon receipt of the “Pass Token”, the device starts data
transmission.