stm32f407vg spi1 data register stay 0xff

[Jalal Sadigli]

Posted on May 02, 2017 at 10:53

hi, i am new to community.....

i have a stm32f4 discovery board with sym32f407cg microcontroller i tried to test spi communucation of the microcontroller with onboard accelerometer

but there is one or more problem that i can not hande

the problem is whatever i write on data register of spi1 , the register only shows 0xff when i read it with the help of pointer

how can i solve this problem

thats what i did as settings of spi1..

spi_cr1 |= 0x30; // select speed

spi_cr1 |= 0x03; // select cpha and cpol

spi_cr1 |= 0x00; // select dff

spi_cr1 |= 0x00; // select msbfirst

spi_cr2 |= 0x10; // select frf

spi_cr2 |= 0x04; // set ssoe

spi_cr1 |= 0x04; // set mstr

spi_cr1 |= 0x40; // enable spi

##discovery ##spi #stm32

[waclawek.jan]

Posted on May 02, 2017 at 12:28

The SPI_DR is in fact two registers: when you write it, it is the transmit buffer; when you read it, it is the receive buffer. Thus you read always what you've received last.

JW

[Jalal Sadigli]

Posted on May 02, 2017 at 13:13

Thanks for your reply

But the problem is when i write 0x20 to data register ,it shows 0xff on dr

[waclawek.jan]

Posted on May 02, 2017 at 13:29

That's it - you'll never read back the data you've written into SPI_DR, except if you loop back MOSI into MISO externally.

JW

[Tesla DeLorean]

Posted on May 03, 2017 at 01:16

What version of the board do you have? Which accelerometer does it use?

Is this an official ST board, or a clone?

[Jalal Sadigli]

Posted on May 03, 2017 at 10:36

it is probably cloned one because i have bought it from china.

the accelerometer is 

LIS3DSH

how to check version of board?

[Tesla DeLorean]

Posted on May 03, 2017 at 17:28

The colour of the board, buttons, and audio jack should be consistent with this image. The version is in the top corner, the newer boards have ''STM32F407G-DISC1'' silk-screened in the top-left corner, and a board ♯ MB997D

[Jalal Sadigli]

Posted on May 07, 2017 at 19:22

i have solved the problem....

the problem is spi does not communicate correctly because of reasons

***the ti frame format has its own cpha cpol settings which controlled by hardware and can not controlled through cr1 register

***rxne and txe flag should be checked with busy flag . because txe flag set after data transfered to shift register but transmission is not finnished

and also before setting cs pin  low the busy flag must be checked

[Andrei Chichak]

Posted on May 07, 2017 at 20:14

Each slave chip manufacturer is free to choose the cpha and cpol settings. Each master manufacturer is free to choose how to express the phase and polarity. 

Beware, there is a bunch of documentation problems with this accelerometer.

I wrote a series of articles on SPI in general and the LIS3DSH on the F4Discovery in specific. See 

http://embedded.fm/blog/2017/4/26/i-apply-spi-good-vibrations

 and the two previous articles.

Andrei