SPI Receive - pulse in MOSI line

sreyas40 · ‎2025-11-21

The above image represents logic analyzer output when HAL_SPI_Receive_DMA is executed. My doubt is regarding the single high pulse at MOSI line. During HAL_SPI_Transmit_DMA , no issues. Is this normal behaviour? STM as Full duplex master, i have disconnected the slave to check if it was responsible for the high pulse.

Andrew Neil · ‎2025-11-21

Please show your code.

How to insert source code

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

AScha.3 · ‎2025-11-21

For a Full duplex master you should always use TransmitReceive , as the SPI shifts out and in same time.

or with dma: HAL_SPI_TransmitReceive_DMA( ..)

(only receive on full duplex is like : receive and dont care about transmit... :)

It might send anything, maybe the remains from last receive, as you write nothing to send.)

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Ozone · ‎2025-11-21

MOSI is "Master Out Slave In".
What you see on this line is what was written by your code to the SPI Tx register beforehand.