How to send additional bit?

[John Doe1]

Posted on February 06, 2017 at 18:09

Hello,

I'm trying to implement a software that will allow me to send additional one pulse (on the data wire and clock wire). After one pulse I should send data (32 bits) over spi.

Frame should look like:

1 bit + 32 bit

clock pulse every bit

I tried to send 0x80 over SPI and USART but no luck - for 0x80 i have 8 clock pulses. How to implement one clock pulse? PWM? Timers? Dma? 

I would be grateful for every idea !

John

#solution-needed #idea-needed

[howard n2wx]

Posted on February 06, 2017 at 18:18

Momentarily flip the data and clock lines into GPIO mode and as outputs, start a timer for one bit time, flip them back when the timer runs? 

[John Doe1]

Posted on February 06, 2017 at 18:28

Thanks, that's a good idea but using that solution i'll propably lose on performance for a larger sets of data.

[howard n2wx]

Posted on February 06, 2017 at 18:55

Does your part's USART support 9 bit mode?

[John Doe1]

Posted on February 06, 2017 at 18:33

I would like to mention that SPI is not required. It's about synchronized data send (one bit per one clock pulse)

[John Doe1]

Posted on February 06, 2017 at 19:41

Is there no solution to generate synchronized PWM with clock pin?

[Tesla DeLorean]

Posted on February 06, 2017 at 22:30

No, the peripherals are of pretty simple and limited functionality. Want to do odd things, use an FPGA/CPLD

Want to send 8x 33-bit values, have the SPI DMA 33x 8-bit values where your 32-bit data is slewed across the buffer.

Use TIM1/8 in One-Pulse, 33x Repetition (or x66 for transitions), and DMA to GPIOx->BSRR, from a pattern buffer.

[John Doe1]

Posted on February 08, 2017 at 20:18

8x33-bit? You mean 33 bytes?

[Andrew Kitaev]

Posted on February 09, 2017 at 13:59

I had a similar task.

One solution is to switch to 11-bit mode and send three 'words' of 11 bits. Of course with prior bit shifting and splitting of original 32-bit data.

[waclawek.jan]

Posted on February 09, 2017 at 14:41

 ,

 ,

The 3x11 trick may be nice but possible only on newer STM32s which have more flexible setting than the '

SPI which allows only 8 or 16 bit frames.

JW