ReadFD(TPCANHandle)

def ReadFD(
    self,
    Channel)

The return value is a 3-touple. The order of the returned values is as follow: 

[0]: The method's return value as a TPCANStatus code. PCAN_ERROR_OK is returned on success. The typical errors in case of failure are:  

[1]: A TPCANMsgFD structure with the CAN message read. 

[2]: A TPCANTimestampFD value with the time when a message was read. 

The use of Read and ReadFD are mutually exclusive. The PCAN Channel passed to this method must be initialized using InitializeFD (plain function: CAN_InitializeFD). Otherwise the error PCAN_ERROR_ILLOPERATION is returned. 

The ReadFD method returns received messages or status messages from the receive queue. It is important to call ReadFD repeatedly until the queue is empty. In case there are no more messages in queue, the value PCAN_ERROR_QRCVEMPTY is returned. The error code PCAN_ERROR_QRCVEMPTY is also returned if the reception of messages is disabled. See Receive Status Parameter for more information. 

The receive queue can contain up to 32767 messages. 

There are two possibilities for reading messages from the receive queue of a Channel: 

Time-Triggered Reading: Consists in periodically calls to the ReadFD method. Typically, an application start a timer that every 50 or 100 milliseconds check for messages, calling the ReadFD method in a loop until the value of PCAN_ERROR_QRCVEMTY or another error condition is reached. 

Event-Triggered Reading: Consists in reacting to a notification sent by the PCAN driver to a registered application, when a message is received and inserted in its receive queue. See Using Events to obtain more information about reading with events. 

About bus errors / Status messages 

If a bus-off error occur, an application cannot use the channel to communicate anymore, until the CAN controller is reset. With PCAN-Basic it is not possible to reset the CAN controller through a function directly. Consider using the PCAN-Basic property PCAN_BUSOFF_AUTORESET which instructs the API to automatically reset the CAN controller when a bus-off state is detected. 

Another way to reset errors like BUSOFF, BUSWARNING, and BUSPASSIVE, is to uninitialize and initialise again the channel used. This causes a hardware reset. 

The message type (see TPCANMessageType) of a CAN message indicates if the message is a 11-bit, 29-bit, FD, RTR, Error, or Status message. This value should be checked every time a message has been read successfully. 

If the bit PCAN_MESSAGE_ERRFRAME is set in the TPCANMsg.MSGTYPE field, the message is an Error frame (see Error Frames). 

If the bit PCAN_MESSAGE_STATUS is set in the TPCANMsg.MSGTYPE field, the message is a Status message. The ID and DLC fields do not contain valid data. The first 4 data bytes of the message contain the Error Code. The MSB of the Error Code is in data byte 0, the LSB is in data byte 3. If a status message was read the return value of ReadFD is also the error code. 

Examples:

Python Notes

• Class-Method: Unlike the .NET Framework, under Python a variable has to be instantiated with an object of type PCANBasic in order to use the API functionality.
• Python's first argument convention: Under Python, 'self' is a parameter that is automatically included within the call of this method, within a PCANBasic object and hasn't to be indicated in a method call. This parameter represents the calling object itself.

The following example shows the use of method ReadFD on the channel PCAN_USBBUS1. In case of failure, the returned code will be translated to a text (according with the operating system language) in English, German, Italian, French or Spanish, and it will be shown to the user. 

Note: It is assumed that the channel was already initialized using the method InitializeFD and that the following code is executed periodically. 

Python:  

readResult = PCAN_ERROR_OK,
while (readResult[0] & PCAN_ERROR_QRCVEMPTY) != PCAN_ERROR_QRCVEMPTY:
    # Check the receive queue for new messages
    #
    readResult = objPCAN.ReadFD(PCAN_USBBUS1)
    if readResult[0] != PCAN_ERROR_QRCVEMPTY:
        # Process the received message
        #
        print "A message was received"
        ProcessMessage(result[1],result[2]) # Possible processing function, ProcessMessage(msg,timestamp)
    else:
        # An error occurred, get a text describing the error and show it
        #
        result = objPCAN.GetErrorText(readResult[0])
        print result[1]
        HandleReadError(readResult[0]) # Possible errors handling function, HandleError(function_result)

WriteFD 

Using Events 

Error Frames 

Plain function Version: CAN_ReadFD