Hello,
I am using an STM32H7 MCU with STM32CubeIDE to communicate with a BiSS-C encoder in SPI RXONLY Master mode.
My goal is to generate 64 SCK clocks every 10ms without delay.
However, I am observing the following issue:
Each time I call HAL_SPI_Receive(), SCK stays low for around 10 microseconds before the clock output starts.
This happens regardless of SPI speed.
At 1MHz SPI clock, the delay is around 10us.
At 2MHz SPI clock, the delay reduces to about 5us.
But there is always some delay before the first SCK pulse.
The same code and settings on an STM32F103 board do not show this delay.
I already tried RXONLY and FULLDUPLEX modes, manual NSS control, enabling and disabling NSS Pulse mode, but the result is the same.
SPI settings:
hspi1.Instance = SPI1;
hspi1.Init.Mode = SPI_MODE_MASTER;
hspi1.Init.Direction = SPI_DIRECTION_2LINES_RXONLY;
hspi1.Init.DataSize = SPI_DATASIZE_8BIT;
hspi1.Init.CLKPolarity = SPI_POLARITY_LOW;
hspi1.Init.CLKPhase = SPI_PHASE_1EDGE;
hspi1.Init.NSS = SPI_NSS_SOFT;
hspi1.Init.BaudRatePrescaler = SPI_BAUDRATEPRESCALER_128;
hspi1.Init.FirstBit = SPI_FIRSTBIT_MSB;
hspi1.Init.TIMode = SPI_TIMODE_DISABLE;
hspi1.Init.CRCCalculation = SPI_CRCCALCULATION_DISABLE;
hspi1.Init.CRCPolynomial = 0x0;
hspi1.Init.NSSPMode = SPI_NSS_PULSE_DISABLE;
hspi1.Init.NSSPolarity = SPI_NSS_POLARITY_HIGH;
hspi1.Init.FifoThreshold = SPI_FIFO_THRESHOLD_01DATA;
hspi1.Init.TxCRCInitializationPattern = SPI_CRC_INITIALIZATION_ALL_ZERO_PATTERN;
hspi1.Init.RxCRCInitializationPattern = SPI_CRC_INITIALIZATION_ALL_ZERO_PATTERN;
hspi1.Init.MasterSSIdleness = SPI_MASTER_SS_IDLENESS_00CYCLE;
hspi1.Init.MasterInterDataIdleness = SPI_MASTER_INTERDATA_IDLENESS_00CYCLE;
hspi1.Init.MasterReceiverAutoSusp = SPI_MASTER_RX_AUTOSUSP_DISABLE;
hspi1.Init.MasterKeepIOState = SPI_MASTER_KEEP_IO_STATE_DISABLE;
hspi1.Init.IOSwap = SPI_IO_SWAP_DISABLE;Question:
Is there any way to eliminate or reduce this initial SCK low time (~10us) before data transmission starts?
Thanks in advance for your help
Edited to apply source code formatting - please see How to insert source code for future reference.
