Should the GPIO pins toggle when transmitting CAN1 (STM32F4discovery)

[Aart Scheepers]

Posted on November 15, 2017 at 22:40

I am trying to make the can interface work on the STM32F4Discovery board.

I did create a project with Cube, and noted CAN1 as being on PD0 and 1.

Then I created a can message and am trying to send it through CAN1 with HAL_CAN_Transmit...

My circuit, only the pins PD0 and 1 are pulled up to 3V, rest is left alone , as I want to see something happen on those pins.

I see in the debugger that:

1) When pulling down PD0 or PD1, CAN does not initialize - It fails with timeout in the initialization of the hardware

2) When pulling up PD0 and PD1, CAN does initialize

3) When doing the HAL_CAN_Transmit, it fails with a timeout.

If I connect a oscilloscope on the PD0 and 1, they are both high and do not toggle; nothing happens.

Question: Without anything connected to the pins except a pullup (2k resistor) should I expect something to happen?

This is my code for trying to send messages:

CanTxMsgTypeDef mes;

    mes.DLC = 8; //Length of data    mes.Data[0] = 0;    mes.ExtId = 1;    mes.IDE = CAN_ID_STD;    mes.RTR = CAN_RTR_DATA;    mes.StdId = 1;    hcan1.pTxMsg = &mes;    /* Infinite loop */    /* USER CODE BEGIN WHILE */    while (1) {        /* USER CODE END WHILE */        HAL_CAN_Transmit(&hcan1, 100);        /* USER CODE BEGIN 3 */

    }

I added a zip file with the src and inc folder of my project...

What is the best way to proceed here? Do I need some more circuitry, to get things going?

Thanks for pointing me into the right direction.

#can-communitation #stm32f4discovery

[Tesla DeLorean · Accepted solution]

Posted on November 16, 2017 at 01:14

You need transceiver where CANRX can see what CANTX is driving on the bus, and then you'll need a receiving device to acknowledge reception of the packet.

Look at schematics for the EVAL series boards, and other threads on forum.

[Aart Scheepers]

Posted on November 19, 2017 at 11:05

This was usefull. I added a small circuitry, with a pullup to VDD, with 1k resistor and diodes on the TX pins so they can pulldown the can bus.

The signals start coming up, and with 2 nodes I see the other node acknowledging the can message.

(Next step is to add a 1051 can controller)

Great, thanks!