Read Procedure for PCF8574A

[Sherif8]

Hello Everyone,

I'm on a project that uses PCF8574A for I/O Expansion.

The controller is LM3S6918, the interface is BitBanging I2C.

I've succeeded in the write part, stuck in the read part.

will paste the code used for the read..

int main(void)
{
 	IOX_Init(0);                              //Board Initializations
	StartCondition();
//	WriteByteToIOX(0x62);              //The writing commands which have been successful
//	halMcuWaitUs(30);
	WriteIntoPortB();                      //Got a free port on the controller, connected it with the outputs of the PCF8574A
	ReadByteFromIOX();                  //The problematic scheme
	StopCondition();

	while(1);
}

void IOX_Init(S_DB_Interface_t *interface)
{
        //Whatever
}

void StartCondition(void)
{
        //Whatever
}

void StopCondition(void)
{
        //Whatever
}

void WriteIntoPortB(void)
{
	GPIOPinWrite(GPIO_PORTB_BASE, GPIO_PIN_1, GPIO_PIN_1);
	GPIOPinWrite(GPIO_PORTB_BASE, GPIO_PIN_3, GPIO_PIN_3);
	GPIOPinWrite(GPIO_PORTB_BASE, GPIO_PIN_5, GPIO_PIN_5);
	GPIOPinWrite(GPIO_PORTB_BASE, GPIO_PIN_0, 0);
	GPIOPinWrite(GPIO_PORTB_BASE, GPIO_PIN_2, 0);
	GPIOPinWrite(GPIO_PORTB_BASE, GPIO_PIN_4, 0);
	GPIOPinWrite(GPIO_PORTB_BASE, GPIO_PIN_6, 0);
}


void ReadByteFromIOX(void)
{
	static unsigned char NewByte;
	unsigned char x;
	char i;
	for(i = 0; i < 8; i++)
	{
		WriteBitToIOX(ReadSlaveAdd & 0x80);    //Send the read add, 0x79, the A2 is one, Both A1 and A0 are zeros
		ReadSlaveAdd <<= 1;
	}

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

	halMcuWaitUs(10);

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

	halMcuWaitUs(30);

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

        //Change the direction of SDA pin into input
	GPIODirModeSet(GPIO_PORTA_BASE, GPIO_PIN_3, GPIO_DIR_MODE_IN);

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

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

	halMcuWaitUs(10);

	//Drive SDA LOW
        //As a receiver, the master should pull the SDA LOW to inform the ack
	GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_3, 0);

	halMcuWaitUs(30);

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

	halMcuWaitUs(30);
}

unsigned char ReadBitFromIOX(void)
{
	unsigned char NewBit;
	
        //Drive SCL LOW        
        GPIOPinWrite(GPIO_PORTA_BASE, GPIO_PIN_6, 0);

        halMcuWaitUs(30);

	NewBit = GPIOPinRead(GPIO_PORTA_BASE, GPIO_PIN_3) & 0x08;

         halMcuWaitUs(60);

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

	return NewBit;
}

Please note that i use the same ack scheme in the write and read and it works for the write.
The NewByte char is always zeros

Thanks a lot,
Sherif