STM CircleOS forum / CAN_BS1 and CAN_BS2

kounst · 2010-05-08 17:48:53

I might be wrong but I think you also have to add 1 to TS1 and TS2.

CAN_BS1 = TS1 +1;
CAN_BS1 = TS2 +1;

At least that way it worked for me.

Regards,
kounst

Last edited by kounst (2010-05-08 17:49:21)

Matthias · 2010-05-08 21:12:38

have you entered the right frequency?
What hardware do you use?

I use the following values

#ifdef _125KB
CAN_InitStructure.CAN_Prescaler = 16;
CAN_InitStructure.CAN_BS1 = 8;
CAN_InitStructure.CAN_BS2 = 7;
#endif
#ifdef _250KB
CAN_InitStructure.CAN_Prescaler = 8;
CAN_InitStructure.CAN_BS1 = 8;
CAN_InitStructure.CAN_BS2 = 7;
#endif
#ifdef _500KB
CAN_InitStructure.CAN_Prescaler = 4;
CAN_InitStructure.CAN_BS1 = 8;
CAN_InitStructure.CAN_BS2 = 7;
#endif
#ifdef _1000KB
CAN_InitStructure.CAN_Prescaler = 2;
CAN_InitStructure.CAN_BS1 = 8;
CAN_InitStructure.CAN_BS2 = 7;
#endif

Last edited by Matthias (2010-05-08 21:28:02)

kounst · 2010-05-09 13:30:21

my apb1 frequency is 18MHz
I'm using an STM32F103VCT6. It's not a primer but that shouldn't make a difference.

Your spreadsheet calculated the following:

BaudRate BRP[9:0] TS1[3:0] TS2[2:0] SAMPLE POINT
500.000 1 8 7 44,4%
500.000 1 9 6 38,9%
500.000 1 10 5 33,3%
500.000 1 11 4 27,8%
500.000 1 12 3 22,2%
500.000 1 13 2 16,7%
500.000 1 14 1 11,1%
500.000 1 15 0 5,6%
500.000 2 8 1 16,7%
500.000 2 9 0 8,3%
500.000 3 0 6 77,8%
500.000 3 1 5 66,7% <--
500.000 3 2 4 55,6%
500.000 3 3 3 44,4%
500.000 3 4 2 33,3%
500.000 3 5 1 22,2%
500.000 3 6 0 11,1%
500.000 8 0 1 50,0%
500.000 8 1 0 25,0%

this way it didn't work
CAN_InitStructure.CAN_SJW = CAN_SJW_1tq;
CAN_InitStructure.CAN_BS1 = CAN_BS1_1tq;
CAN_InitStructure.CAN_BS2 = CAN_BS2_5tq;
CAN_InitStructure.CAN_Prescaler = 4;

this way it does
CAN_InitStructure.CAN_SJW = CAN_SJW_1tq;
CAN_InitStructure.CAN_BS1 = CAN_BS1_2tq;
CAN_InitStructure.CAN_BS2 = CAN_BS2_6tq;
CAN_InitStructure.CAN_Prescaler = 4;

same thing with 250kbaud

See also reference manual page 562 figure 205:
BS1 = tq * (TS1 +1)
BS2 = tq * (TS2 +1)

Matthias · 2010-05-09 20:12:52

Here is the error:
see stm32f10x_can.h
definatsion the other is when the value 1TG = 0, 2TG = 1, etc

#define CAN_BS1_1tq ((uint8_t)0x00) /* 1 time quantum */
#define CAN_BS1_2tq ((uint8_t)0x01) /* 2 time quantum */
.
.
#define CAN_BS1_15tq ((uint8_t)0x0E) /* 15 time quantum */
#define CAN_BS1_16tq ((uint8_t)0x0F) /* 16 time quantum */

kounst · 2010-05-09 22:32:40

So you are saying that there is a bug in the stm32f10x_can.h file:
#define CAN_BS1_1tq ((uint8_t)0x00) /* 1 time quantum */
instead of
#define CAN_BS1_1tq ((uint8_t)0x01) /* 1 time quantum */

As a workaround you have to add 1 not only to BRP but also to TS1 and TS2.

You should edit your projects description accordingly

Regards

# 1 2010-05-08 17:48:53 CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

# 2 2010-05-08 21:12:38 CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

Re: CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

# 3 2010-05-09 13:30:21 CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

Re: CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

# 4 2010-05-09 20:12:52 CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

Re: CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

# 5 2010-05-09 22:32:40 CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

Re: CAN_BS1 and CAN_BS2 (project: STM32 CAN baudrate calculation 1.0)

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