Hi All, I need to transfer 24 bit of data through STM 32 SPI , the challenge is that the IP only allow to transfer 8 or 16 bit of data .

[RSree.1]

Things that have tried.

1. Used the GPIO as chip select . In this configuration , the width of chip selected pulse is more than expected. ( Attached oscilloscope short for your reference ).

Kindly requesting to sent the procedure or sample code to sent 24 bit of data through STM32 SPI

[TDK]

Send 8 bits of data 3 times in succession. That will give you 24 bits of data. On some families, you can send 24 bits in a single operation.

If you want super tight timing of the CS line, you can make your own SPI driver. HAL has a lot of overhead. You can also compile on higher optimization levels. But CS being low for longer poses no problems for communication.

Include your chip number in your post.

[waclawek.jan]

What STM32?

And what system clock? It seems to me that even with Cube/HAL, 20us-60us between setting GPIO and any other action is too much.

As TDK said, get rid of Cube and switch on optimization.

JW

[RSree.1]

Hi All,

Really thanks for your quick response ,please find the inline answers.

>>Include your chip number in your post.

STM32F746IGTx

LQFP176

The SPI interface chip is ADAR 1000.

https://www.analog.com/en/products/adar1000.html

>> And what system clock?

Internal 16 Mhz clock , attached screen shot for the clock configuration.

So with my understanding from the above reply .

1. it is not possible to generate a 24 bit of data through the SPI IP ( Attached IP setting) and require to write own SPI logic ?

>> If the answer is yes , any example is available for reference ?

1. Can I use the SPI DMA function (HAL_SPI_Transmit_DMA(hspi, pData, Size) ), for this requirement .

Lastly apology , if I am asking silly question as I am new to STM32 Microcontroller.

Regards,

Rs

[TDK]

Sending 3 8-bit bytes adds up to 24 bits. There is no functional difference between a single 24-bit write and 3x8-bit writes.

The F7 has a 32-bit TXFIFO which can buffer the 3 bytes immediately without having to wait for data to be shifted out.

You can use DMA if you want, but it's not necessary.

[RSree.1]

Hi ,

Please find the inline answers.

>>Sending 3 8-bit bytes adds up to 24 bits. There is no functional difference between a single 24-bit write and 3x8-bit writes.

When sending 3 8 bits, the chip select is asserted for two times ( attached screen shot ) , so my peripheral chip is assuming a different SPI cycle during the assertion of each chip select. That is the problem, I am facing

[TDK]

Looks like you're using NSSP mode.

Manage CS as a GPIO output and toggle it manually.

[RSree.1]

Hi ,

Thanks for the answer. Please find the inline answers.

>>Looks like you're using NSSP mode.

Yes , the screenshot provided is in NSSP mode.

>>Manage CS as a GPIO output and toggle it manually.

Yes , I have tried to toggle manually . But the issue is that the CS to assert is taking long time. Attached the screen shot for reference .

Any idea how to reduce the assertion time ?

The code I was using given below.

HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_SET);

         HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_RESET);

         HAL_SPI_Transmit(&hspi1,(uint8_t *) &EEPROM_WRDI , 1, 100);

         HAL_GPIO_WritePin(GPIOA, GPIO_PIN_4, GPIO_PIN_SET);

Really glad for your help.

[TDK]

> Any idea how to reduce the assertion time ?

Use your own code driver instead of HAL, or increase optimization level and/or clock frequency.

If you want the convenience of HAL, you live with its drawbacks.