DCAN
CAN_TX
CAN Core
Rx Tx
Pin
CAN_RX
Pin
Functional Description
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23.3.8.3.3 External Loopback Mode
The external loopback mode is similar to the loopback mode; however, it includes the signal path from
CAN core to Tx pin, the Tx pin itself, and the signal path from Tx pin back to CAN core. When external
loopback mode is selected, the input of the CAN core is connected to the input buffer of the Tx pin.
With this configuration, the Tx pin IO circuit can be tested.
External loopback mode can be activated by setting bit ExL in test register to one.
Figure 23-7 shows the connection of signals CAN_TX and CAN_RX to the CAN core in external loopback
mode.
NOTE: When loopback mode is active (LBack bit set), the ExL bit will be ignored.
Figure 23-7. CAN Core in External Loopback Mode
23.3.8.3.4 Loopback Mode Combined With Silent Mode
It is also possible to combine loopback mode and silent mode by setting bits LBack and Silent at the same
time. This mode can be used for a “Hot Selftest,” i.e., the DCAN hardware can be tested without affecting
the CAN network. In this mode, the CAN_RX pin is disconnected from the CAN core and no dominant bits
will be sent on the CAN_TX pin.
Figure 23-8 shows the connection of the signals CAN_TX and CAN_RX to the CAN core in case of the
combination of loopback mode with silent mode.
3892
Controller Area Network (CAN) SPRUH73H–October 2011–Revised April 2013
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