xPC Target

Introduction

xPC Target CAN-AC2 supports CAN specification 2.0a and 2.0b but this does not generally include the CANopen protocol on driver level. Nevertheless it is possible to access CANopen devices by the CAN-AC2 drivers in a general way.

CANopen knows two types of messages ie. SDO and PDO. SDO's are used to setup or initialize a CANopen device for a certain behavior. PDO's are messages which contain real-time data (ie. converted A/D values from a analog input device) and are just regular CAN-type messages with no CANopen object, index and subindex information.

xPC Target application which have to access CANopen devices over the CAN-AC2 drivers transmit SDO's during the initialization phase and the termination phase of the driver. PDO's are sent or received during the simulation phase of the driver.

Because SDO's and PDO's are regular CAN-messages the CAN-AC2 drivers just have to provide a way to transmit SDO's during the initialization and termination phase of the CAN-AC2 setup driver block to initialize the different CANopen devices in the network. This is done by providing a c-file within your project directory which describes the SDO messages to send to setup and terminate the CANopen device. During the compilation stage of the xPC Target application (build-process) this c-file which has to have the file name CANAC2_setup.c is then included into the setup driver.

This implementation has the advantage of accessing a specific CANopen device without the need to have special driver blocks for this device. It is therefore a general implementation but has on the other hand the disadvantage that the user must be able to provide the information (messages) to properly setup and terminate the communication with a specific CANopen device. This information is provided either by the CANopen device manufacturer or by the CAN-CIA association (www.can-cia.de).

To explain how to write the CANAC2_setup.c file for a specific CANopen device an example is shown below. In this example an analog input device from Selectron (www.selectron.ch) with name AIC711 is used to get the A/D-converted values over the CAN-network into the xPC Target application.

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.

• initialization phase - Enable global interrupts to enable asynchronous mode (object 6423) - Put device from pre-operational mode into operational mode (transmission of PDO's starts).
• simulation phase - CAN-AC2 receive driver block outputs the latest received A/D-values.
• termination phase - Put device from operational mode into pre-operational mode (transmission of PDO's stops)

The node id of the AIC711 device is set over DIP-switches and in this example it is assumed that the node id is set to 11 (decimal) and the device is connected to CAN-port 1 of the CAN-AC2-board.

Then the CANAC2_setup.c file could look as follows

///////////////////////////////////////////////////////////////
/
// Number of initialization and termination messages
///////////////////////////////////////////////////////////////
/
#define CANAC2_init_number2
#define CANAC2_term_number1
//#define DEBUG_CANAC2

// do not change the following four lines
#define CANAC2_setup_present
CANAC2_type CANAC2_init[CANAC2_init_number+1];
CANAC2_type CANAC2_term[CANAC2_term_number+1];
int CANAC2_counter;
// 


///////////////////////////////////////////////////////////////
/
// Identifier and constant section
///////////////////////////////////////////////////////////////
/


#define AIC711_node_111
#define AIC711_sdo_base1536
#define MAS_boot     0
///////////////////////////////////////////////////////////////
/
// Initialization section
///////////////////////////////////////////////////////////////
/

// AIC711 SDO object 6423: enable global interupts
CANAC2_init[0].port=1;
CANAC2_init[0].identifier=AIC711_sdo_base+AIC711_node_1;
CANAC2_init[0].data[0]=0x22;
CANAC2_init[0].data[1]=0x23;
CANAC2_init[0].data[2]=0x64;
CANAC2_init[0].data[3]=0x00;
CANAC2_init[0].data[4]=0x01;
CANAC2_init[0].no_bytes=5;
CANAC2_init[0].wait_ms=20;

// put AIC711_node_1 from pre-operational into operational state
CANAC2_init[1].port=1;
CANAC2_init[1].identifier=MAS_boot;
CANAC2_init[1].data[0]=0x01;
CANAC2_init[1].data[1]=AIC711_node_1;
CANAC2_init[1].no_bytes=2;
CANAC2_init[1].wait_ms=20;


///////////////////////////////////////////////////////////////
/
// Termination section
///////////////////////////////////////////////////////////////
/


// put AIC711_node_1 from operational into pre-operational state
CANAC2_term[0].port=1;
CANAC2_term[0].identifier=MAS_boot;
CANAC2_term[0].data[0]=0x80;
CANAC2_term[0].data[1]=AIC711_node_1;
CANAC2_term[0].no_bytes=2;
CANAC2_term[0].wait_ms=20;

As soon as this file is placed into your project directory and the xPC Target application is rebuilt the messages defined above will be sent during initialization and termination phase of the setup driver block.

The SIMULINK-model could look as follows

The receive block will read continuously the object to which the AIC711 sends the PDO's (ie. the converted A/D-values).

Because the output of this block contains the 8 bytes of the received CAN-data as a double value a conversion block (AIC711conversion) is necessary to split the 8 bytes (double) into 4 doubles (output signals) which represent the A/D-value in volts for each of the four analog input channels. The conversion is made according to the data representation of object 6401. Use the aselmasaic711.c file as a template to implement conversion blocks for other CANopen devices. The third channel is then stored with an outport block which can be visualized by the xPC Target scope functionality.

Because CAN-messages with id 0 (boot) and 1536+node_id (SDO) have to be sent and CAN-message with id 640+node_id (PDO) have to be received over CAN-port 1 the dialogue-box of the setup-block has to look as follows:

The receive block receives the data (PDO) over CAN-message 640+node-i and has to look therefore as follows:

If more than one CANopen device is connected to the network the dialogue boxes of the setup and receive block and the CANAC2_setup.c file has to be extended accordingly. If you need for-loops in the CANAC2_setup.c use the variable CANAC2_counter.

If an analog output device (or digital output device) is connected to the network an additional send block has to be dragged into the model to send the PDO's to the newly connected CANopen server.

CAN-AC2 and CANopen devices

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