CAN TX Problem

[randyao12345]

Posted on October 01, 2014 at 19:44

Hi ST Forum,

Debugging a CAN TX message and can't really do it :(. I connected scope to PB13 and just see a high (3V) signal on the TX line. Anything wrong with my code below?I'm wondering if it's my CAN_mode. Can anyone tell me what's the difference between normal mode, silent mode and loopback mode?Thanks,#include <stm32f4xx_can.h>#include <stm32f4xx_gpio.h>#include <stm32f4xx_rcc.h>#include <semihosting.h>GPIO_InitTypeDef GPIO_InitStructure;CAN_InitTypeDef CAN_InitStructure;CanTxMsg Message1;CanTxMsg Message2;void CANInit(void);void Message(void);int main(void){ CANInit(); Message();    while(1)    {    CAN_Transmit(CAN2,&Message1);    }}void CANInit(void){ RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOB,ENABLE); RCC_APB1PeriphClockCmd(RCC_APB1Periph_CAN2,ENABLE); GPIO_InitStructure.GPIO_Pin = GPIO_Pin_12 | GPIO_Pin_13; GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF; GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz; GPIO_Init(GPIOB,&GPIO_InitStructure); GPIO_PinAFConfig(GPIOB,GPIO_PinSource12,GPIO_AF_CAN2); //CAN_RX = PB12 GPIO_PinAFConfig(GPIOB,GPIO_PinSource13,GPIO_AF_CAN2); //CAN_TX = PB13 /* CAN2 reset */ /* CAN2 configuration */ CAN_DeInit(CAN2); //De-initialize CAN 2 to start over CAN_InitStructure.CAN_TTCM = DISABLE; // time-triggered communication mode = DISABLED CAN_InitStructure.CAN_ABOM = DISABLE; // automatic bus-off management mode = DISABLED CAN_InitStructure.CAN_AWUM = DISABLE; // automatic wake-up mode = DISABLED CAN_InitStructure.CAN_NART = DISABLE; // non-automatic retransmission mode = DISABLED CAN_InitStructure.CAN_RFLM = DISABLE; // receive FIFO locked mode = DISABLED CAN_InitStructure.CAN_TXFP = DISABLE; // transmit FIFO priority = DISABLED CAN_InitStructure.CAN_Mode = CAN_Mode_Silent; // normal CAN mode CAN_InitStructure.CAN_SJW = CAN_SJW_1tq; // synchronization jump width = 1 CAN_InitStructure.CAN_BS1 = CAN_BS1_6tq; //14 CAN_InitStructure.CAN_BS2 = CAN_BS2_8tq; //6 CAN_InitStructure.CAN_Prescaler = 2; // baudrate 125kbps //CAN_InitStructure.CAN_Prescaler = 4; // baudrate 500 kbps CAN_Init(CAN2, &CAN_InitStructure);}void Message(void){ Message1.RTR = CAN_RTR_Data; //transmit data (master to slave) remote frame is a destination node requesting data Message1.IDE = CAN_Id_Standard; //Standard identifier length Message1.StdId = 0x7FF; //Identifier and priority Message1.DLC = 1; //8 bit data Message1.Data[0] = (uint8_t)0xAA; //actual message}

[Tesla DeLorean]

Posted on October 01, 2014 at 20:10

In Loopback mode you can test the CAN absent any other devices, in Normal mode when you TX there needs to be an RX device attached to the bus.

[randyao12345]

Posted on October 01, 2014 at 20:23

Oh thanks Clive. So if I switch to loopback mode I should be able to see the CAN frame on the oscilloscope?

Do you see anything else wrong about my code?Thanks.

[Tesla DeLorean]

Posted on October 01, 2014 at 21:45

Hard to say, I've posted working CAN code, so I'm not going to try and decompose this.

CAN2 is slaved off CAN1, I don't think your baud rate will be what your comments suggest. Pay attention to the APB bus speed, the prescaler, and bit quanta. A working CAN interface will require a receiver and transmitter, along with bus transceivers at both ends.