Specifications

CAN-AC2 and CANopen devices
16-19
Restriction: CANopen initialization and termination is only supported if the
CAN-AC2 board is equipped with the Philips C200 controller for standard
identifiers.
Example: Accessing the AIC711 CANopen device from Selectron
The AIC711 contains four analog input channels with a resolution of 12bits and
a minimal update-time (sample time) of 10ms.
As explained in earlier chapters the CAN-AC2 drivers use the dynamic object
model to reach low latency times. Therefore the A/D values from the AIC711
have to be received in such a way that it is compatible to the object model of the
driver.
The AIC711 has to be seen as a CANopen server and the xPC Target CAN-AC2
drivers (the xPC Target application) as a CANopen client. The AIC711 offers to
way of getting the converted A/D-values over the network:
•synchronous
•asynchronous
In the synchronous mode the client transmits a remote frame to the server to
invoke an A/D-conversion of a specified channel. It then has to wait (poll) until
the converted value is received by an ordinary CAN data-message which will
contain the values. This mode leads to large latency times up to 20ms
(Tsmin=10ms). During this time period the xPC Target gets stucked and this
is inacceptable.
On the other hand the synchronious mode fits not well into the dynamic object
model implementation of the xPC Target CAN-drivers because remote frames
have to be transmitted.
In the asynchronous mode the AIC711 sends PDO’s automatically in a regular
manner to the client. A certain change of an analog input value invokes
automatically an A/D-conversion and after conversion a PDO-message is
constructed and sent automatically to the client. This mode fits very well into
the object model of the drivers. Therefore the CANopen devices should always
be used in asynchronous mode if used together with xPC Target.
Regarding to the information in the AIC711 CANopen manual (provided by
Selectron) the following initialization messages (SDO’s) and termination
messages (SDO’s) have to be invoked.