SPI driven 74595 shift register produces random output

[Stipe]

Hi folks,

For the past 2 days, i tried to setup a simple SPI communication to feed a shift register with 7-segment data.

I already have done this in the arduino IDE, using shiftOut.

Now I want to make this more elegant with the CubeIDE. I set up an SPI1 and connected it to the SER input. Clk also connected to SPI Clk. I habe even a separate GPIO pin for the shift register latch SRCLK.

Here is some code (it should count from 0-9, the segment data is in the digArray):

 spiBuffer[0] = digArray[count++];
 if (count==10) {
   count=0;
 }

 HAL_GPIO_WritePin(SRCLK_GPIO_Port, SRCLK_Pin, GPIO_PIN_RESET);
 HAL_SPI_Transmit(&hspi1, spiBuffer, 1, 10);
 HAL_GPIO_WritePin(SRCLK_GPIO_Port, SRCLK_Pin, GPIO_PIN_SET);

The thing is, the 7-segment displays almost always random ***. I measured every signal with oscilloscope.

The SPI is setup with MSB first which is like in my Arduino program. I struggle with the clock (I think it should have some "delay" and we need a rising edge). I set polarity low and high, dont know what is correct. I think it should be high. Nothing works.

Is there a known issue about SPI and shift registers? I tried to lower the baudrate ridiculously, that was not the problem.

Anyone an idea? Thanks for your comments!

PS:  I think I connected everything very well, even verified each segment connection. The result is quite random (yes, every open input is connected on the 74hc595).

[MM..1]

Is your 595 on 5V or 3V3 ?

[Stipe]

Everything is 3.3V supplied. That worked fine in my old arduino setup...

[MM..1]

Then HC is ok and you only require scope signals and setup SPI config right.

Too good practice is check return value from 

HAL_SPI_Transmit(&hspi1, spiBuffer, 1, 10);

[Stipe · Accepted solution]

Thanks for the hint. I think it's any hardware issue. The scope looks good:

Edit:

The problem was that I swapped RCLK and SRCLK pins. I hate the data sheet, the description says 

RCLK

12

14

I

RCLK Input

SRCLK

11

14

I

SRCLK Input

Man, this is not very helpful actually 8-(