Reading Second Byte from PCF8575

[Sherif8]

I'm using PCF8575 with LM3S6965 via bitbanging I2C. I read the first byte very accurately but having a problem reading the second one. I always get 0xff for the second. What I'm actually doing is that I first write to the port a random value like 0x7988 then the reading interrupt is activated to supposedly read the same value.

This is a piece of the code i'm running, while the writing occurs flawlessly I haven't it mentioned here:

int main(void)
{
    SysCtlLDOSet(SYSCTL_LDO_2_75V);

    // Set the clocking 50MHz to run directly from the crystal.
    //
    SysCtlClockSet(SYSCTL_SYSDIV_4 | SYSCTL_USE_PLL | SYSCTL_OSC_MAIN | SYSCTL_XTAL_7_37MHZ);

    IOX_Init();
    WriteByteToIOX(0x7988, 0x42);

    while(1);
}


void IOX_Init()
{
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOA | SYSCTL_PERIPH_GPIOC);

    //SCL PA6 & SDA PA3 pins
    GPIOPadConfigSet(GPIO_PORTA_BASE, (GPIO_PIN_3 | GPIO_PIN_6), GPIO_STRENGTH_4MA, GPIO_PIN_TYPE_OD);
    GPIODirModeSet(GPIO_PORTA_BASE, (GPIO_PIN_3 | GPIO_PIN_6), GPIO_DIR_MODE_OUT);
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_PIN_3);
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, GPIO_PIN_6);

    //Interface3GPIO3==> interrupt pin
       //No external pull up
    GPIOPadConfigSet(GPIO_PORTC_BASE, GPIO_PIN_4, GPIO_STRENGTH_4MA, GPIO_PIN_TYPE_STD_WPU);

    GPIOIntTypeSet(GPIO_PORTC_BASE, GPIO_PIN_4, GPIO_BOTH_EDGES);
    GPIOPinIntEnable(GPIO_PORTC_BASE, GPIO_PIN_4);
    GPIOPortIntRegister(GPIO_PORTC_BASE, &ReadHandler);
}


void StartCondition(void)
{
    //Set SDA and SCL HIGH at the same time
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_PIN_3);
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, GPIO_PIN_6);

    halMcuWaitUs(30); //min 4.7usec

    //Drive SDA LOW
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_3, 0);

    halMcuWaitUs(30); //min 4usec

    //Drive SCL LOW
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, 0);

    halMcuWaitUs(30);
}

void StopCondition(void)
{
    GPIODirModeSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_DIR_MODE_OUT);
    GPIOPadConfigSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_STRENGTH_4MA, GPIO_PIN_TYPE_OD);

    //Set SDA and SCL LOW at the same time
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_3, 0);
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, 0);

    halMcuWaitUs(30);

    //Drive SCL HIGH
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, GPIO_PIN_6);

    halMcuWaitUs(30);

    //Drive SDA HIGH
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_PIN_3);

    halMcuWaitUs(30);

    //Drive SCL LOW
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, 0);
}

void ReadHandler(void)
{
    unsigned int data = 0;
    //Clear INT bit
    GPIOPinIntClear(GPIO_PORTC_BASE, GPIO_PIN_4);

    data=ReadByteFromIOX(0x43);
}


unsigned int ReadByteFromIOX(unsigned char readslaveadd)
{
    unsigned char x;
    unsigned int newdata = 0;
    unsigned char i;

    StartCondition();

    for(i = 0; i < 8; i++)
    {
        WriteBitToIOX(readslaveadd & 0x80);
        readslaveadd <<= 1;
    }

    GPIOPadConfigSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_STRENGTH_4MA, GPIO_PIN_TYPE_STD);
    GPIODirModeSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_DIR_MODE_IN);

    //Handle the ACK
    //Drive SCL LOW
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, 0);
    halMcuWaitUs(60);

    //Drive SCL HIGH
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, GPIO_PIN_6);
    halMcuWaitUs(60);

    for (i = 0; i < 8; i++)
    {
        x = ReadBitFromIOX();
        if(x)
        {
            newdata <<= 1;
            newdata |= 0x01;
        }
        else
            newdata <<= 1;
    }

    //Handle the ACK
    GPIOPadConfigSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_STRENGTH_4MA, GPIO_PIN_TYPE_OD);
    GPIODirModeSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_DIR_MODE_OUT);

    //Drive SCL LOW
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, 0);
//  halMcuWaitUs(30);

    //Ack from master on the recived data
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_3, 0);
    halMcuWaitUs(60);

    //Drive SCL HIGH
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, GPIO_PIN_6);
    halMcuWaitUs(60);

    GPIOPadConfigSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_STRENGTH_4MA, GPIO_PIN_TYPE_STD);
    GPIODirModeSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_DIR_MODE_IN);

    if(readslaveadd == ReadSlaveAdd5)   //5th IOX is 8 bit only
        return (newdata);

    for (i = 0; i < 8; i++)      //others are 16 bit
    {
        x = ReadBitFromIOX();
        if(x)
        {
            newdata <<= 1;
            newdata |= 0x01;
        }
        else
            newdata <<= 1;
    }

    halMcuWaitUs(60);
    GPIOPadConfigSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_STRENGTH_4MA, GPIO_PIN_TYPE_OD);
    GPIODirModeSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_DIR_MODE_OUT);

    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, 0);
    halMcuWaitUs(30);
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_PIN_3);
    halMcuWaitUs(30);
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, GPIO_PIN_6);
    halMcuWaitUs(60);

    StopCondition();

    return (newdata);
}

unsigned char ReadBitFromIOX(void)
{
    unsigned char NewBit;

    //Ensure SCL is LOW
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, 0);
    halMcuWaitUs(30);

    NewBit = GPIOPinRead(GPIO_PORTA_BASE, GPIO_PIN_3) & GPIO_PIN_3;
    halMcuWaitUs(30);

    //Drive SCL HIGH to begin transfer
    GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, GPIO_PIN_6);
    halMcuWaitUs(60);

    return NewBit;
}


void halMcuWaitUs(unsigned int uDelay)
{
    SysCtlDelay((SysCtlClockGet()/3000000)*uDelay);
}

Also, I'm attaching a picture of the waveform of the serial clock and data lines.