CAN bus Issue.

Wilson Martinez

We are having some issues in setting the eCAN on the TMS320F28335.

First, the following snippet code is for setting the baud rate but it does not generate 500 kbps. Are we missing something to set the baud rate to 500 kbps?

// The following block for all 150 MHz SYSCLKOUT
    // (75 MHz CAN clock) - default. Bit rate = 500 kbps See Note at End of File
    //
    // BitTime = CAN Module Clock Frequency / (BRP * Bitrate)
    //
    // BitTime = 75e6/(10 *5e5) = 15TQ
    //
    // BitTime = TSEG1 + TSEG2 + 1
    //
    // 15TQ = 8TQ + 6TQ + 1
    ECanaShadow.CANBTC.bit.BRPREG = 10;
    ECanaShadow.CANBTC.bit.TSEG2REG = 5;
    ECanaShadow.CANBTC.bit.TSEG1REG = 7;

Secondly, we have just tested the transmission so far. If there is not another node in the bus and hence the device is not receiving and ACK, the CAN bus keeps transmitting the can frame forever. Is that the normal behavior? Can we control how many times the re-transmission happen?

I'll appreciate any advise.

Best,

Wilson

over 2 years ago

0 Wilson Martinez over 2 years ago

Intellectual 255 points

The snipped code above is generating the 500 kbps but the right setting (which don't work) should be as follow:

+1 Hareesh Janakiraman over 2 years ago in reply to Wilson Martinez

TI__Guru* 95315 points

Wilson,

Please download my Application report http://www.ti.com/lit/SPRA876 . It has many tested examples. I also request you to look at the Debug tips provided. Most CAN issues can be resolved by going through this checklist.

Wilson Martinez said:
ECanaShadow.CANBTC.bit.BRPREG = 10;
ECanaShadow.CANBTC.bit.TSEG2REG = 5;
ECanaShadow.CANBTC.bit.TSEG1REG = 7;

Note that the value of BRPreg, TSEG1reg & TSEG2reg are all enhanced by 1 when the module uses these values for calculation. If you want an effective BRP of 10, you should write 9 in BRPreg. This is explained in the TRM. Please see page 812 of www.ti.com/lit/SPRUI07.

Wilson Martinez said:
If there is not another node in the bus and hence the device is not receiving and ACK, the CAN bus keeps transmitting the can frame forever. Is that the normal behavior?

Yes, this is the normal behavior.

Wilson Martinez said:
Can we control how many times the re-transmission happen?

No.

+1 Hareesh Janakiraman over 2 years ago in reply to Hareesh Janakiraman

TI__Guru* 95315 points

Wilson,

In CAN, transmission is not considered successful unless the reception is successful. Reception is considered successful when at least one node received the transmitted frame without any errors and transmitted the ACK bit to the transmitter. I have explained this in my Application report.

The TRM chapter explains the CAN protocol implementation in the MCU. i.e. it explains the functions of the various registers/bits. However, it does not explain the protocol itself. For protocol information, refer to these excellent videos:

https://training.ti.com/automotive-can-overview

https://training.ti.com/ti-precision-labs-canlinsbc-can-and-can-fd-protocol?context=1139747-1138099-1139707-1138111

https://training.ti.com/ti-precision-labs-canlinsbc-can-and-can-fd-overview?context=1139747-1138099-1139707-1138109

https://training.ti.com/ti-precision-labs-canlinsbc-can-physical-layer?context=1139747-1138099-1139707-1138110