Festo Электромотор MTR-DCI - Manual (Page 29)

1. System overview
1-7 Festo P.BE-MTR-DCI-DN-EN en 1209a
I/O Messaging I/O messages are sent by a participant and can be received
and processed by one or more other participants. For I/O
messages, the following dialogues between the participants
are possible:
– The slaves can be cyclically queries by the master
(polled I/O) or
– the messages are cyclically sent from the master or
slave, or sent when a state change occurs (COS/Cyclic) or
– all slaves are queried by the master with a single com-
mand (bit-strobe, not supported by the MTR-DCI).
The data field contains exclusively user data, protocol data
is not specified. All information required for using the data
is stored in the assigned “Connection Object”.
Up to 64 fieldbus nodes can be operated via the serial
CAN bus in a DeviceNet network. The expansion of the net-
work depends on the selected bit rate (125 kbps, 250 kbps or
500 kbps). DeviceNet telegrams contain up to 8 bytes of user
data. If it is necessary to exchange larger amounts of data,
then before sending the data has to be broken down by
means of fragmentation, transmitted sequentially, and then
put together again in the recipient.
In contrast to other Fieldbus systems, the messages are
identified and not the bus participants. The participants may
send messages when the bus is free. Every bus participant
decides when they want to send data or request other bus
participants to send data. Bus conflicts are resolved by
assigning a particular priority (Connection ID) to the mess-
ages. The smaller the identifier, the higher the priority. Before
DeviceNet devices can exchange messages using these IDs,
they must first be appropriately configured.