Performance Motion Devices Prodigy Series User Manual page 67

3.5.2 PRP Messages over CANbus
If the Prodigy/CME PC/104 card is set up to process PRP command messages from a host controller over CANbus,
a specific format for the packets must be followed. This section describes the format of how PRP messages are carried
over CANbus.
Since native CANbus communications can not be larger than 8 bytes, hosting the PRP system, which can support
shorter as well as longer messages, requires additional layers to manage data segmentation and desegmentation. The
protocol that is used by the Prodigy/CME PC/104 cards to accomplish this is very similar to the SDO (Service Data
Object) protocol of the CANopen standard.
The details of this protocol are extensive enough that they are not described here, but are available in the Prodigy/CME
Programmer's Reference.
3.5.2.1 CANbus packet processing
Unlike the serial protocols, the SDO based CANbus protocol has a robust error checking and retransmission mecha-
nism built in that corrects for garbled or otherwise unusable transmissions.
Nevertheless, if a host controller does not receive the complete response packet within a specific time window (com-
munications timeout), then the original message should be resent.
3.5.3 PRP Messages over Ethernet
The existence of ports, and the broad range of packet lengths that are supported with the Ethernet protocol, makes
sending PRP messages very simple. For both sent and received messages the PRP message is simply loaded as the
'payload' of the Ethernet message. The only convention that must be observed is that the host controller's destination
TCP port must be equal to the Prodigy/CME PC/104 card's TCP default value set using the
Note that the UDP protocol may not be used for PRP communications to/from the Prodigy/CME PC/104 card.
3.5.3.1 Ethernet packet processing
Unlike the serial protocols, Ethernet TCP packets have a robust error checking and retransmission mechanism built
in that corrects for garbled or otherwise unusable transmissions.
Prodigy/CME PC/104 User's Guide
Accessing Card Resources
command.
SetDefault
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