TLC5947: Unexpected BLANK pin behavior

Thank you for the fast response!

Here is the implementation from the library:

void Adafruit_TLC5947::write(void) {
  // digitalWrite(_ena, HIGH);
  digitalWrite(_lat, LOW);
  // 24 channels per TLC5974
  for (int16_t c=24*numdrivers - 1; c >= 0 ; c--) {
    // 12 bits per channel, send MSB first
    for (int8_t b=11; b>=0; b--) {
      digitalWrite(_clk, LOW);
      
      if (pwmbuffer[c] & (1 << b))  
        digitalWrite(_dat, HIGH);
      else
        digitalWrite(_dat, LOW);

      digitalWrite(_clk, HIGH);
    }
  }
  digitalWrite(_clk, LOW);
  
  digitalWrite(_lat, HIGH);  
  digitalWrite(_lat, LOW);
  // digitalWrite(_ena, LOW);
}

As you can see on the first and last lines, I set the BLANK pin (_ena in this case) HIGH before the data is propagated and back to LOW after it is latched. Right now it is commented out, which is what causes the awesome response in 2/3 of the SPI chains but the bizarre random behavior in the other SPI chain. When the lines are uncommented, 3/3 SPI chains display the correct LED values, but with a visible blink at each transition as expected. My goal is to try to get the third SPI chain to behave like the first two which show no blinking when the LEDs transition states.

I have tried switching the digital pins assigned to each SPI chain, thinking that it was a problem with the microcontroller, but the effect is the same.

Hi Kenneth, sorry for my slow reply.

Thank you for the code sample. I'm fairly new to all this, so I apologize, but I wasn't able to find the code for driving 2 TLC5947s. In main.c I noticed that the method for sending data was a bit different than what I had implemented, so I will give that a try, but I didn't see anything specific to 2 TLC5947s. It would be great if you could point me to a particular file!

Also, I don't know that this will answer why sometimes even chained TLC5947s respond very well without any blinking when the data is being written while others behave randomly unless the LAT pin is held low. I know there are lots of possible variables, but I was wondering if you had any insight into that behavior.

The chips are great and I would love to be able to solve this problem!

Thanks again for your help.