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FS6500  CAN communication in Debug Mode

Question asked by Jyothsna Rajan on Oct 3, 2018
Latest reply on Oct 12, 2018 by Jyothsna Rajan

I have an FS6500 connected to MPC5746 and want to test the CAN communication via the FS6500 CAN interface.


Section 11.6 /page 31 the FS6500 Datasheet Rev3.0 states that

"In debug mode, the CAN transceiver is set to normal operation mode by default allowing CAN communication without SPI configuration."  


Following the directions mentioned in AN5238 (reproduced here for convenience) I connected the 10K Dbg_Rpu resistor

After reading the above two, it seemed that I do not have to do any prior configuration of the FS6500.@ If I put the SBC in debug mode and configure the CAN interface on the MPC, and connect the TX/RX between the MPC and FS6500, I should be able to send/receive messages via the FS65xx CAN interface.


I created a simple program that

- initializes MPC CAN interfaces CAN_1 (connected to FS65xx) and CAN2(connected to external CAN transceiver) 

- sends a CAN message through each of the two interfaces.

Other than the I/O port/pad mux configuration, all configuration(CAN_CTRL1, RX/TX MB etc)are the same for both the interfaces.


CAN1 communication does not work - I do not see any output from the FS65xx CAN transceiver. I confirmed that MPC outputs TX data and on the FS65xx, data arrives at pins 20(TxD) but there is no output on pins 8/9 - the CANH/CANL  outputs. The problem appears to be localized to the FS65xx chip 


CAN-2 works as expected.


1. Has anyone tried exercising the CAN interface on the FS65xx when it is in debug mode, without doing any prior configuration via software? 


2. How do we know for sure that FS65xx is in debug mode?


3. If the FS65xx is wired as above, for debug mode and no other configuration has been done, what should be the values of these bits if I read the register over DSPI:

a) DBG_HW bit (bit 0 )of HW_CONFIG register

b) CAN_Mode_1, CAN_MODE_0 and CAN_AUTO_DIS (bits 7:5) of CAN_MODE register


4. If setup is required even if debug mode, what is the minimal configuration that must be done. 


I need to determine if the chip is bad or if it is only some missing configuration. If you have an example, that would be very helpful.


Thank you for suggestions.