CANopen communication
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05/16/2007
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In addition, the
PDO Communication Parameters
allow you to define under which
conditions a PDO is to be transmitted and when a transmitted value is to be
processed internally:
•
Synchronous transmission
:
In this case a node, the
SYNC Producer
, periodically sends an SYNC
message, with which the message transmission can be synchronized
network-wide. In the case of a PDO that is configured for synchronous
transmission, sending and processing of the received data are linked to the
SYNC message.
•
Asynchronous transmission
:
The transmission of data is not linked to the SYNC message. It is event-
controlled.
In this way a Transmit PDO can be configured event-controlled. In this case, the PDO
is sent if the parameter value transmitted in the PDO has changed. Alternatively, a
PDO can be sent if the transmission is requested by a SYNC message. Synchronous
processing of a PDO can also be configured on the receive side. This means that the
data are only processed when the next SYNC message is received. In this way,
several drives can be started simultaneously, for example.
PDOs may only be transmitted when a slave is in
"OPERATIONAL"
status. In
"PRE-
OPERATIONAL"
status, the PDO mapping and transmission type can be set for each
SDO, before the slave switches over to
OPERATIONAL
status and the PDO
transmission begins.
4.2.2.2.1 Request PDOs: Remote Transmission Request
A PDO consumer can request PDO messages from a PDO producer via the
Remote
Transmission Request
. To do this, the consumer sends a message with the COB-ID
of the requested PDO, in which case the RTR bit of the CAN message is set to 1. This
denotes a PDO request. If the PDO producer is configured (transmission type), so that
it will react to such requests, it sends the relevant PDO, in which case the RTR bit is
set to 0.