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STM32F103 SPI configuration troubles

Question asked by Carlo Agrusti on Apr 24, 2017
Latest reply on Apr 26, 2017 by Carlo Agrusti

Hi all,


I'm having hard times in configuring SPI communication with a M95128 eeprom; I'm using SPI1 on a STM32F103 mcu, with following connection scheme:

PA.04 -> ~S (CS)

PA.05 -> C (CLK)

PA.06 -> Q (MISO)

PA.07 -> D (MOSI)


and here follows my configuration code snippet:


* enable APB2 peripheral clock for SPI1

RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1, ENABLE);
* configure pins used for SPI1
* PA.04 = CS
* PA.05 = SCK
* PA.06 = MISO (Master In/Slave Out)
* PA.07 = MOSI (Master Out/Slave In)

GPIO_InitStruct.GPIO_Pin = GPIO_Pin_7 | GPIO_Pin_5;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF_PP;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStruct);
GPIO_InitStruct.GPIO_Pin = GPIO_Pin_6;
GPIO_Init(GPIOA, &GPIO_InitStruct);
* The MISO, MOSI and CLK pins are now connected to their AF
* so that the SPI1 can take over control of the pins

GPIO_PinLockConfig(GPIOA, GPIO_Pin_5);
GPIO_PinLockConfig(GPIOA, GPIO_Pin_6);
GPIO_PinLockConfig(GPIOA, GPIO_Pin_7);
* configure CS (PA.04) as output Open Drain

GPIO_InitStruct.GPIO_Pin = GPIO_Pin_4;
GPIO_InitStruct.GPIO_Mode = GPIO_Mode_Out_OD;
GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStruct);
GPIOA->BSRR = GPIO_Pin_4; // set CS (PA.04) high
* configure SPI1 in Mode 0
* CPOL = 0 --> clock is low when idle
* CPHA = 0 --> data is sampled at the first edge

SPI_InitStruct.SPI_Direction = SPI_Direction_2Lines_FullDuplex; // set to full duplex mode, seperate MOSI and MISO lines
SPI_InitStruct.SPI_Mode = SPI_Mode_Master; // transmit in master mode, NSS pin has to be always high
SPI_InitStruct.SPI_DataSize = SPI_DataSize_8b; // one packet of data is 8 bits wide
SPI_InitStruct.SPI_CPOL = SPI_CPOL_Low; // clock is low when idle
SPI_InitStruct.SPI_CPHA = SPI_CPHA_1Edge; // data sampled at first edge
SPI_InitStruct.SPI_NSS = SPI_NSS_Soft; // set the NSS management to internal and pull internal NSS high
SPI_InitStruct.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_256; // SPI frequency is APB2 frequency / 16 (4.5MHz)
SPI_InitStruct.SPI_FirstBit = SPI_FirstBit_MSB; // data is transmitted MSB first
SPI_Init(SPI1, &SPI_InitStruct);
SPI_Cmd(SPI1, ENABLE); // enable SPI1

When I try to send a read status register instruction to the eeprom, I can see that the CLK correctly sends 8 pulses while the MOSI line stays stuck at 1, as shown by attached picture, thus resulting in a 0xFF sent to the eeprom instead of 0x05 (which is the opcode for read status register).


Any hint?