SPI for reading bits in Half-duplex

[parisa]

Posted on January 10, 2017 at 10:07

Hi,

I should read output data from an IC with SPI protocol as shown below.Actually I've got confused how can read each bits with SPI for (n=16 to 32). Or can we another simple approach to read data?

I did some settings but I know it is completely wrong to read these bits because most of the time clock is available and not when I need to read.

   SPI_InitStructure.SPI_Direction = SPI_Direction_1Line_Rx;

  SPI_InitStructure.SPI_Mode = SPI_Mode_Master;  SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;   SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;  SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;  SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_64;  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;  SPI_InitStructure.SPI_CRCPolynomial = 7;  SPI_Init(SPI3, &SPI_InitStructure);

[waclawek.jan]

Posted on January 10, 2017 at 11:16

SPI_InitStructure.SPI_Direction = SPI_Direction_1Line_Rx;

Don't use the halfduplex Rx-Only mode. Use the normal fullduplex mode - you don't need to assign a MOSI pin and it still will work. Then, simply transmit+receive 4 bytes or 2 halfwords.

JW

[parisa]

Posted on January 10, 2017 at 12:40

Thanks

Waclawek.Jan

for your explanation

Actually I access only to output data-pin (because the chip sends only data and don't receive anythings)

I changed my normal full-duplex mode and write this program , but I get p[0]=227 or 160 and p[1]=0 always ( in 16bit that is wrong value when the IC change it's value)

#include <stdio.h>

#include <string.h> #include ''stm32f10x_gpio.h'' #include ''stm32f10x_rcc.h'' #include ''stm32f10x_usart.h'' #include ''stm32f10x_spi.h'' #define SPI_FLASH SPI3 #define SPI_CLK RCC_APB1Periph_SPI3 #define SPI_GPIO GPIOC #define SPI_GPIO_CLK RCC_APB2Periph_GPIOC #define SPI_PIN_SCK GPIO_Pin_10 #define SPI_PIN_MISO GPIO_Pin_11 #define SPI_PIN_MOSI GPIO_Pin_12 void SPIConfig(void){ SPI_InitTypeDef SPI_InitStructure; GPIO_InitTypeDef GPIO_InitStructure; /* Enable SPI and GPIO clocks */ RCC_APB2PeriphClockCmd( SPI_GPIO_CLK , ENABLE); RCC_APB1PeriphClockCmd(RCC_APB1Periph_SPI3,ENABLE); GPIO_PinRemapConfig(GPIO_Remap_SPI3, ENABLE); /* Configure SPI pins: SCK, MISO and MOSI */ GPIO_InitStructure.GPIO_Pin = SPI_PIN_SCK | SPI_PIN_MISO | SPI_PIN_MOSI; GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP; GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz; GPIO_Init(SPI_GPIO, &GPIO_InitStructure); SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex; SPI_InitStructure.SPI_Mode = SPI_Mode_Master; SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b; SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low; SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge; SPI_InitStructure.SPI_NSS = SPI_NSS_Soft; SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_64; SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB; SPI_InitStructure.SPI_CRCPolynomial = 7; SPI_Init(SPI3, &SPI_InitStructure); /* Enable the SPI */ SPI_Cmd(SPI3, ENABLE); } void delay(){ int i,j; for(i=0;i<10000;i++) for(j=0;j<250;j++); } int main(){ unsgined char p[3] SPIConfig(); while(1){ delay();delay(); while (SPI_I2S_GetFlagStatus(SPI3, SPI_I2S_FLAG_TXE) == RESET); SPI_I2S_SendData(SPI3,0xff); if(SPI_I2S_GetFlagStatus(SPI3, SPI_I2S_FLAG_RXNE) == SET){ p[0]=SPI_I2S_ReceiveData(SPI3);} while (SPI_I2S_GetFlagStatus(SPI3, SPI_I2S_FLAG_TXE) == RESET); SPI_I2S_SendData(SPI3,0xff); if(SPI_I2S_GetFlagStatus(SPI3, SPI_I2S_FLAG_RXNE) == SET){ p[1]=SPI_I2S_ReceiveData(SPI3); } //print to terminal p[1] and p[0] } }

[waclawek.jan]

Posted on January 10, 2017 at 13:03

I guess this is the time when you should connect an oscilloscope or a logic analyzer.

JW

[parisa]

Posted on January 10, 2017 at 20:17

Thanks waclawek.jan for your suggestion.

I've seen that my IC works fine when I set SPI data size to 16b.However my main problem is that in this code , I am able to read the first two bytes and when I want to read the next two byte it return again the two first bytes.(it seems that clock stop for a little time (when I want to get p[1] value)and the IC thinks it is a new connection) and I get p[0] is equal to p[1].

♯ include <stdio.h> ♯ include <string.h> ♯ include 'stm32f10x_gpio.h' ♯ include 'stm32f10x_rcc.h' ♯ include 'stm32f10x_usart.h' ♯ include 'stm32f10x_spi.h' ♯ define SPI_FLASH           SPI3 ♯ define SPI_CLK             RCC_APB1Periph_SPI3 ♯ define SPI_GPIO                GPIOC ♯ define SPI_GPIO_CLK        RCC_APB2Periph_GPIOC ♯ define SPI_PIN_SCK         GPIO_Pin_10 ♯ define SPI_PIN_MISO        GPIO_Pin_11 ♯ define SPI_PIN_MOSI        GPIO_Pin_12void SPIConfig(void){SPI_InitTypeDef  SPI_InitStructure;  GPIO_InitTypeDef GPIO_InitStructure;  /* Enable SPI and GPIO clocks */  RCC_APB2PeriphClockCmd( SPI_GPIO_CLK , ENABLE);RCC_APB1PeriphClockCmd(RCC_APB1Periph_SPI3,ENABLE);  GPIO_PinRemapConfig(GPIO_Remap_SPI3, ENABLE);  /* Configure SPI pins: SCK, MISO and MOSI */  GPIO_InitStructure.GPIO_Pin = SPI_PIN_SCK | SPI_PIN_MISO | SPI_PIN_MOSI;  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;  GPIO_Init(SPI_GPIO, &GPIO_InitStructure);        SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;  SPI_InitStructure.SPI_Mode = SPI_Mode_Master;  SPI_InitStructure.SPI_DataSize = SPI_DataSize_16b; SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;  SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;  SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_64;  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;  SPI_InitStructure.SPI_CRCPolynomial = 7;  SPI_Init(SPI3, &SPI_InitStructure);  /* Enable the SPI  */  SPI_Cmd(SPI3, ENABLE);}    void delay(){    int i,j;    for(i=0;i<10000;i++)    for(j=0;j<250;j++);}int main(){    unsgined char p[3]    SPIConfig();                    while(1){                delay();delay();    while (SPI_I2S_GetFlagStatus(SPI3, SPI_I2S_FLAG_TXE) == RESET);    SPI_I2S_SendData(SPI3,0xffff);    if(SPI_I2S_GetFlagStatus(SPI3, SPI_I2S_FLAG_RXNE) == SET){    p[0]=SPI_I2S_ReceiveData(SPI3);}    while (SPI_I2S_GetFlagStatus(SPI3, SPI_I2S_FLAG_TXE) == RESET);        SPI_I2S_SendData(SPI3,0xff);        if(SPI_I2S_GetFlagStatus(SPI3, SPI_I2S_FLAG_RXNE) == SET){    p[1]=SPI_I2S_ReceiveData(SPI3);    }    //print to terminal p[1] and p[0]        }    }

How can solve this states?

[parisa]

Posted on January 10, 2017 at 20:57

Something like this: