37.5.1.8 Test Modes

To enable write access to the TEST register, the CCCR.TEST bit (CCCR <7>) must be set to ‘1’. This allows the configuration of the test modes and test functions.

Four output functions are available for the CAN transmit pin, CANx_TX, by programming the TEST.TX bits (TEST <6:5>). Additionally to its default function, the serial data output, it can drive the CAN Sample Point signal to monitor the CAN’s bit timing and it can drive constant dominant or recessive values. The actual value at the CANx_RX pin can be read from the TEST.RX bit (TEST <7>). Both functions can be used to check the CAN bus physical layer.

Due to the synchronization mechanism between the GCLK_CANx and CLK_CANx_AHB domains, there may be a delay of several CLK_CANx_AHB periods between writing to the TEST.TX bits (TEST <6:5>) until the new configuration is visible at the output pin, CANx_TX. This also applies when reading the input pin, CANx_RX, through the TEST.RX bit (TEST <7>).

Note: Test modes must be used for production tests or self test only. The software control for the CANx_TX pin interferes with all CAN protocol functions. It is not recommended to use test modes for application.