Sending ten bits to SPI slave

[paul2]

Posted on October 18, 2014 at 20:19

Hi,

I want to send ten bits from my STM32F4 Discovery to a SPI slave.

The SPI Init struct only allows 8- or 16 bit (SPI_DataSize_8b, SPI_DataSize_16b)

Whats the best way to send the required ten bits to the SPI slave?

Thanks.

[Tesla DeLorean]

Posted on October 18, 2014 at 23:26

Send as 40-bits (5 x 8-bit), or bit bang

[paul2]

Posted on October 19, 2014 at 08:26

Hi Clive,

Is there a typical SPI bit-banging example available?

Thanks.

[paul2]

Posted on October 21, 2014 at 21:43

Hi,

to send SPI data I use the code below:

GPIOE->BSRRH |= GPIO_Pin_13; 
received_val=SPI2_send(0x16); 
GPIOE->BSRRL |= GPIO_Pin_13;

The problem is the CS (GPIO_Pin_13) already becomes high at the rising edge of the last CLK pulse. I have implemented several checks (code below) to make sure the data has been send before raising the CS signal again.

while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_TXE) == RESET);
SPI_I2S_SendData(SPI2, data / 256);
// be sure that the character goes to the shift register
while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_TXE) == RESET);
SPI_I2S_SendData(SPI2, data);
// be sure that the character goes to the shift register
while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_TXE) == RESET);
// and then be sure it has been sent over the wire
while (SPI_I2S_GetFlagStatus(SPI2, SPI_I2S_FLAG_BSY) == SET);

Whats the best solution in order prevent the CS level already going high at the rising edge of the last CLK pulse? Thanks.