Custom_Element is the structure defined in user_define.h.Custom_Element is also shown in Figure 2-6.

Origin Identifier indicates the origin of the message. The following are the examples of Origin Identifier (CAN_ID_LENGTH =0,SPI_ID_LENGTH =4).

• Example 1: CAN interface receive and transmit
  1. When the CAN-SPI bridge receives a CAN message, the ID from CAN frame is Origin Identifier, indicating where the message comes from.
  2. When the CAN-SPI bridge transmits a CAN message, Origin Identifier is ignored (CAN_ID_LENGTH is set to 0 default).
• Example 2: SPI Interface Receive and Transmit (SPI protocol transmission)
  1. When the CAN-SPI bridge receives an SPI message (SPI protocol transmission), DEFAULT_SPI_ORIGIN_ID is the Origin Identifier since the SPI does not have an ID.
  2. When the CAN-SPI bridge transmits the SPI message(SPI protocol transmission), Origin Identifier is a 4-byte ID in SPI data (SPI_ID_LENGTH is set to four as the default), indicating where the message came from.
• Example 3 - SPI interface receives and transmits (SPI transparent transmission)
  1. When the CAN-SPI bridge receives an SPI message (SPI transparent transmission) DEFAULT_SPI_ORIGIN_ID is the Origin Identifier since SPI does not have an ID.
  2. When the CAN-SPI bridge transmits the SPI message (SPI transparent transmission), Origin Identifier is ignored. (Transparent transmission does not have an ID area).

Destination Identifier indicates the destination of the message.

• Example 1 - CAN interface receive and transmit
  1. When a CAN-SPI bridge receives a CAN message, DEFAULT_CAN_DESTINATION_ID is the Destination Identifier since CAN_ID_LENGTH is set to 0 as the default. SPI transmit does not require an ID.
  2. When the CAN-SPI bridge transmits a CAN message, Destination Identifier is the CAN ID in CAN frame. In this example, 11 bit or 29 bit are both supported.
• Example 2 - SPI interface receive and transmit (SPI protocol transmission)
  1. When the CAN-SPI bridge receives an SPI message (SPI protocol transmission), 4-byte ID from the SPI data is Destination Identifier(SPI _ID_LENGTH is set to 4 default). CAN transmit requires ID information.
  2. When the CAN-SPI bridge transmits an SPI message (SPI protocol transmission), Destination Identifier is ignored since SPI transmit does not require an ID.
• Example 3 - SPI interface receive and transmit (SPI transparent transmission)
  1. When the CAN-SPI bridge receives an SPI message (SPI transparent transmission), DEFAULT_SPI_DESTINATION_ID is the Destination Identifier (Transparent transmission does not have ID area). CAN transmit requires ID information.
  2. When the CAN-SPI bridge transmits a SPI message (SPI transparent transmission), Destination Identifier is ignored since SPI transmit does not require an ID.

/*user-defined information storage structure */
typedef struct {
    /*! Origin Identifier, indicating the origin of the message */
    uint32_t origin_id;
    /*! Destination Identifier, indicating the destination of the message */
    uint32_t destination_id;
    /*! Data Length Code */
    uint8_t dlc;
    /*! Data bytes */
    uint8_t data[TRANSMIT_DATA_LENGTH];
} Custom_Element;