i2csiteb.c

ADS1241与MSP430F449接口设计

#include "hpa449lib.h"
/*****************************************************************************
**	[File]
**	i2cSiteB.c
** [Purpose]
**	Generate I2C protocol using bit banging on ports
**	[Changes]
**	16.06.2002 Roger Neumair
**		started
** 04/08/26 GH
**   implemented both I2C busses on HPA449, fixed some bugs
**	
*/

// site B P2.0(SCL) and P2.1(SDA)
#define SCL_B 0x01
#define SDA_B 0x02
#define I2C_B_OUTP P2OUT
#define I2C_B_DIR  P2DIR
#define I2C_B_IN   P2IN

// Standard implementation SCL and SDA drive low and high impedance;
void I2C_B_Init(void)
{
	// Initialize the port for use with I2C
	// Set direction of SDA and SCL to input to drive it high through pullup
	I2C_B_DIR  &= ~(SDA_B | SCL_B);
	// Set output bit to low (drives only 0 if switched to output direction)
	I2C_B_OUTP &= ~(SDA_B | SCL_B);	
}


void I2C_B_Wait(void)
{
	// check for I2C wait states
	// If slave drives SCL low wait until it releases the SCL line
	I2C_B_DIR &= ~SCL_B;		// SCL is input
	while(!(I2C_B_IN & SCL_B))
		;			// Wait for slave to release SCL
}

void I2C_B_Start(void)
{
	// Set direction of SDA and SCL to input to drive it high through pullup
	I2C_B_DIR &= ~(SDA_B | SCL_B);
	I2C_B_DIR |= SDA_B;		// START condition. Drive SDA low while SCL high
 	I2C_B_DIR |= SCL_B;		// now drive SCL low
}

// Generate a STOP condition on the I2C bus
void I2C_B_Stop(void)
{
   I2C_B_DIR |=  SDA_B;   // make sure SDA is low
	I2C_B_DIR &= ~SCL_B;   
	I2C_B_DIR &= ~SDA_B;
}

//----------------------------------------------------------------------------
// [function]
// I2C_B_SendByte
// [Purpose]
// Sends a byte on the I2C port on site B
// [parameters]
// byte: the byte to send
// [returns]
// true if the addressed device acknoledges
// false if the address device times out acknowledging
// [remarks]
// -
int I2C_B_SendByte(unsigned char byte)
{
	int n, ack;
	unsigned char mask = 0x80;		// Start with MSB

	for(n=7; n>=0; n--)			   // Process 8 bits 
	{
		if((byte & mask) != 0)		// bit is high
		{
			I2C_B_DIR &= ~SDA_B;	   // Set SDA
		}
		else				            // bit is low
		{
			I2C_B_DIR |=  SDA_B;		// Reset SDA
		}
		I2C_B_Wait();			
		I2C_B_DIR |= SCL_B;			// get ready for next bit
		mask >>= 1;			         // shift mask one bit right
	}
	
	I2C_B_DIR &= ~SDA_B;	         // make sure SDA is an input when testing ACK

	// Acknowledge
	I2C_B_Wait();	
	// Last clock cycle
	ack = (I2C_B_IN & SDA_B) ? 0 : 1;
	// set clock back to 0
	I2C_B_DIR |= SCL_B;		
	
	return ack;
}

//----------------------------------------------------------------------------
// [function]
// I2C_B_ReceiveByte
// [Purpose]
// Receives a byte on the I2C port on site B
// [parameters]
// ack: acknowledge 
// [returns]
// byte received
// [remarks]
// -
unsigned char I2C_B_ReceiveByte(int fAck)
{
	int n;
	unsigned char ByteReceived = 0;
	unsigned char mask = 0x80;
	for(n=7; n>=0; n--)			// Process 8 bits 
	{
		I2C_B_Wait();
		if (I2C_B_IN & SDA_B)
			ByteReceived |= mask;		
		I2C_B_DIR |= SCL_B;			// get ready for next bit
		mask >>= 1;			// shift mask one bit right
	}

	// Acknowledge
	if (fAck)
		I2C_B_DIR |=  SDA_B;		// pull SDA low
	else
		I2C_B_DIR &= ~SDA_B;
		
	I2C_B_Wait();
	I2C_B_DIR |= SCL_B;		
	// release SDA
	I2C_B_DIR &= ~ SDA_B;
	return ByteReceived;
}