I'm using MPC5775K to test FlexCAN module now,but I have a lot of questions in the loopback mode,the datasheet said that The Rx CAN input pin is ignored and the Tx CAN output goes to the recessive state (logic '1'),does it means that after I transmit a frame of data ,I should change the state of Tx from output to input? Thank you!!!
You need not change the state of pins. The loopback mode is used for internal test, for example testing of receive/masking operation. FlexCAN behaves as it normally does when transmitting and treats its own transmitted message as a message received from a remote node. The ACK field is ignored so the message can be received normally.
In the loopback mode no message is visible on TX output, it goes to the recessive state (logic “1”).