CANopen Programmer's Manual - Maccon.de

1: Introduction CANopen Programmer’s Manual
PDOs: Description and Examples
Overview
Each amplifier provides eight transmit PDOs and eight receive PDOs. A transmit PDO is used to
transmit information from the device to the network. A receive PDO is used to update the device.
Default PDO Message Identifiers
The Communication Profile reserves four CAN message identifiers for transmit PDOs and four
identifiers for receive PDOs. These addresses are described later in this chapter (see Receive
PDO Communication Parameters, p. 31, and Transmit PDO Communication Parameters, p. 35).
The first four transmit PDOs and receive PDOs provided in Copley Controls CANopen amplifiers
use these default addresses. The addresses of the remaining four transmit PDOs and receive
PDOs are null by default.
The designer can reconfigure any PDO message identifier.
PDO Peer- to-Peer Communication
Peer-to-peer relationships are established by matching the transmit PDO identifier of the sending
node to a receive PDO identifier of one or more other nodes on the network.
Any device can broadcast a PDO message using one of its eight transmit PDOs. The CAN
identifier of the outgoing message matches the ID of the sending PDO. Any node with a matching
receive PDO identifier will accept the message.
PDO Peer-to- Peer Example
For instance, Node 1, transmit PDO 1, has a CAN message ID of 0x0189. Node 2, receive PDO 1
has a matching ID, as does Node 3. They both accept the message. Other nodes do not have a
matching receive PDO, so no other nodes accept the message.
PDO Mapping
PDO mapping allows optimal use of the CAN message’s eight-byte data area.
Mapping uses the SDO to configure dictionary objects in both the sending and the receiving node
to know, for each byte in the PDO message:
The index and sub-index which objects are to be accessed
The type of data
The length of the data
Thus, the PDO message itself carries no transfer control information, leaving all eight bytes
available for data. (Contrast this with the SDO, which uses one byte of the CAN message data
area to describe the objects being written or read, and the length of the data.)
24 Copley Controls