Error initiating microSD card in SPI mode

Question

I am trying to interface a 32 GB microSD card with PIC32MX795F512L using SPI communication. SPI communication is working fine as I have tested it by shorting the Data Input and Output line and receiving back the data which I sent. I am following the examples provided in Lucio de Jasio's book, Programming 32-bit Microcontrollers in C.

Following are the tasks I am performing:

1. Initializing the SPI Communication in initSPI(), setting the baudrate=76 (250 kHz)
2. Initializing the SD card
   -> CS = 1
   -> Sending 80 clock cycles to wake the card
   -> CS = 0
   -> Sending CMD0 command (0x40, 0x00, 0x00, 0x00, 0x00, 0x95)

But the problem is I am not receiving the R1 response from the card, instead I am receiving the 0xFF. Following is the code:

#define FCY 77000000UL
#define FPB (FCY/2)
#define BAUDRATE    9600
#pragma config POSCMOD=HS,FNOSC=PRIPLL
#pragma config FPLLIDIV=DIV_3, FPLLMUL=MUL_21, FPLLODIV=DIV_1
#pragma config FPBDIV=DIV_2, FWDTEN=OFF

#include <stdio.h>
#include <stdlib.h>
#include <plib.h>
#include <stdbool.h>

#define SDI  _RC4
#define SDCS _RA9
#define enableSD()    SDCS = 0
#define disableSD()   SDCS = 1
#define readSPI() writeSPI(0xFF)

int main(int argc, char** argv)
{
    TRISAbits.TRISA9 = 0;   // CS as output
    TRISCbits.TRISC4 = 1;   // SDI as input
    TRISDbits.TRISD0 = 0;   // SDO as output
    TRISDbits.TRISD10 = 0;  // SCK as output
    AD1PCFG = 0xFFFF;
    DDPCONbits.JTAGEN = 0;
    OpenUART1( UART_EN | UART_NO_PAR_8BIT | UART_1STOPBIT, UART_RX_ENABLE | UART_TX_ENABLE, (FPB/16/BAUDRATE)-1 );
    disableSD(); //CS PIN INITIALLY HIGH TO DISABLE CARD
    initSPI();
    initSD();

    while(1)
    {

    }
    return (EXIT_SUCCESS);
}

void initSPI( void)
{
    SPI1BRG = 76; // FPB/154=250KHZ; (76+1)*2 = 154, so brg = 76
    SPI1CONbits.MSTEN = 1; // MasterEnable
    SPI1CONbits.CKE = 1;   // CKE on
    SPI1CONbits.ON = 1;    // SPI Module ON
}

unsigned char writeSPI(unsigned int b)
{
    SPI1BUF=b; // Write to buffer for TX
    while( !SPI1STATbits.SPIRBF)
        ; // Wait transfer complete
    return(SPI1BUF);
}

int initSD(void)
{
    int i,r,rx;
    int data;

    // Step1: Disable SD card
    disableSD();

    // Step2: Send 80 clock cycles to wake up the card
    for(i=0; i<=9; i++)
    {
        data = writeSPI(0xFF);
    }

    // Step3: Enable SD card
    enableSD();

    // Step4: Send CMD0 command to RESET
    r = sendCMD0();
    disableSD();
    if(r!=1)
    {
        putsUART1("CMD reject\n");
    }
}

int sendCMD0()
{
    int i,r;
    enableSD();

    writeSPI(0x40);
    writeSPI(0x00);
    writeSPI(0x00);
    writeSPI(0x00);
    writeSPI(0x00);
    writeSPI(0x95); //CMD0 Command

    for( i=0; i<100; i++)
    {
        r = readSPI();
        if ((r & 0x80) == 0)
            break;
    }
    return ( r);
}

Here is the schematic:

I am not receiving the R1 response. It is stuck at step4 in initSD().

Is there a way I can know if the card has woken up or not after sending 80 clock pulses? After 80 clock pulses, the response from the card is 0xFF.

Do I need to reduce the clock frequency? Currently it's 250 kHz.

Why is the card not initializing. How can I fix it?

Answer 1

Looks on the surface like an electrical problem

• Try a slower speed to start - you may have excessive capacitance in your lines or a slow speed sdCard.
• Are you polling until the card comes ready (see below)
• Can you put a scope on it to check timings, these are critical?
• Try a different SD card, or same card in a working device
• Can you transmit and receive to a different port on same device?
• Can you transmit and receive to a different board using same PIC device?
• Are you using microchip drivers / software libraries?
• Have you got MISO/MOSI correctly wired?
• Are the power requirements met - decoupling caps etc? 10uF+//100nF (some people use 100uF!!)
• Are your output and input pins configured correctly?

At a later stage you may need to check the following - no particular order.

• Check the 'endianness' of your SPI
• Check your CRC
• Double check your protocol

https://www.sdcard.org/downloads/pls/simplified_specs/archive/part1_110.pdf

pg 47 says that you need to poll the device until the card comes ready Are you doing this?

Answer 2

I don't see any code for making the MISO pin an input pin or for making the SCK pin output. Since you aren't using the SPI library in plib, you have to do all the pin initialization yourself. Also, after sending CMD0, increase the number of iterations (in your for loop) from 8 to 20 (I use 100), to provide enough leeway. Also use this comparison instead:

if ((r & 0x80) == 0) 
   break;
return r;

Also make r an unsigned char everywhere.