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STM32F769I-DISCO Driving WS2813b with SPI, MOSI always high

Question asked by Justin Kohlenberg on May 3, 2018
Latest reply on May 3, 2018 by waclawek.jan

I have recently acquired an STM32F769I-Discovery board and am trying to drive a strip of 60 addressable leds (ws2813b).
Because I don't want to use the processor to bit-bang data to the leds (I want the processor free to process other data), I decided to use the SPI peripheral with DMA to create a waveform with the right timings for the ws2813b leds.

I have a working SPI output with the right timing, but the MOSI signal is always high after a transfer completes (I only use the MOSI signal, which connects to the data in of the first LED.

I did some research on the internet and found more people using SPI with DMA to drive these leds, and they fixed this problem by pre- and appending the data with a 0 byte.

I have replicated this pre- and appending of a 0 bytte, but MOSI continues to be pulled high after the last 0 byte (see attached image)

 

I am not that familiar with the hardware, or the SPI protocol, but am hoping some of you can shed some light on this

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