10.1.1 Diagnostic Loopback

The diagnostic loopback or internal loopback function of the SN55HVD233-SEP is enabled with a high-level input on pin 7, LBK. This mode disables the driver output while keeping the bus pins biased to the recessive state. This mode also redirects the D data input (transmit data) through logic to the received data output (R), thus creating an internal loopback of the transmit-to-receive data path. This mimics the loopback that occurs normally with a CAN transceiver because the receiver loops back the driven output to the R (receive data) pin. This mode allows the host microprocessor to input and read back a bit sequence or CAN messages to perform diagnostic routines without disturbing the CAN bus. Figure 33 shows a typical CAN bus application.

If the LBK pin is not used, it may be tied to ground (GND). However, it is pulled low internally (defaults to a low-level input) and may be left open if not in use.

Figure 28. Equivalent Input and Output Schematic Diagrams