Mode of operation of the system
Deutschmann Automation GmbH & Co. KG
18
UNIGATE Fieldbus Gateway CANopen® - ProfibusDP V. 2.3
26.8.11
4.4
Starting phase
During the starting phase the UNIGATE sends the NMT-command "BusStart" every 2 seconds,
that means all connected CANopen®-Slaves are set into the condition "Operational". As soon as
the Gateway has received the first PDO, that is available in the Mapping, this starting phase is
left, which means that the NMT-command is not sent any more. There is no such thing as a
Timeout here since the CANopen®-Slaves do not have to react to this NMT-command. In case a
CANopen®-Slave is later connected in the net, it will consequently not receive this NMT-com-
mand any more. However, it can be re-activated any time through the PB-command-byte (bit 6)
in order to put later CANopen®-Slaves into the condition "Operational".
4.5
Data cycle time
Cycle times of data through the Gateway:
Among other things the actual cycle time of data from CANopen® to Profibus or the other way
round depends on the following parameters:
•
Amount of Mappings
•
Length of the configured Profibus data
•
Amount of COB-IDs used at the Mappings
•
Amount of changed Profibus data between two transmissions
•
Amount of mapped bytes in a COB-ID
•
Baud rate in the Profibus or CAN
On account of the large amount of parameters and their interdependence a formula for the calcu-
lation of the cycle time cannot be stated. From practical measurements cycle times of 100µs up
to 100ms were observed, whereas the maximum Profibus-configuration time of 244 byte I/O and
488 mappings was measured.
In practice, on "regular" conditions,a cycle time of of some milliseconds is to be expected. In
order to optimize the cycle time, the following guidelines should be kept:
•
Amount of Mappings as small as possible
•
Length of the Profibus-configuratio as short as possible
•
Use of all 8 bytes in the COB-IDs if possible => Use of the least possible amount of COB-IDs
