Assembly Implementation

As discussed earler, we can implement I2C by bit-banging on 8051 using any two pins. Here in implementation below we have used P0.0 for SDA (serial data) and P0.1 for SCL (serial clock).

;***************************************
;Ports Used for I2C Communication
;***************************************
	sda equ P0.0
	scl equ P0.1

;***************************************
;Initializing I2C Bus Communication
;***************************************
i2cinit:
	setb sda
	setb scl
	ret

;****************************************
;ReStart Condition for I2C Communication
;****************************************
rstart:
	clr scl
	setb sda
	setb scl
	clr sda
	ret

;****************************************
;Start Condition for I2C Communication
;****************************************
startc:
	setb scl
	clr sda
	clr scl
	ret

;*****************************************
;Stop Condition For I2C Bus
;*****************************************
stop:
	clr scl
	clr sda
	setb scl
	setb sda
	ret

;*****************************************
;Sending Data to slave on I2C bus
;*****************************************
send:
	mov r7,#08
back:
	clr scl
	rlc a
	mov sda,c
	setb scl
	djnz r7,back
	clr scl
	setb sda
	ret

;*****************************************
;ACK and NAK for I2C Bus
;*****************************************
ack:
	clr sda
	setb scl
	clr scl
	setb sda
	ret

nak:
	setb sda
	setb scl
	clr scl
	setb scl
	ret

;*****************************************
;Receiving Data from slave on I2C bus
;*****************************************
recv:
	mov r7,#08
back2:
	clr scl
	setb scl
	mov c,sda
	rlc a
	djnz r7,back2
	clr scl
	setb sda
	ret
		

C Implementation

#define SDA P0_0
#define SCL P0_1

void I2CInit(){
	SDA = 1;
	SCL = 1;
}

void I2CStart(){
	SCL = 1;
	SDA = 0;
	SCL = 0;
}

void I2CRestart(){
	SDA = 1;
	SCL = 1;
	SDA = 0;
}

void I2CStop(){
	SDA = 0;
	SCL = 1;
	SDA = 1;
}

void I2CAck(){
	SDA = 0;
	SCL = 1;
	SCL = 0;
}

void I2CNak(){
	SDA = 1;
	SCL = 1;
	SCL = 0;
}

unsigned char I2CSend(unsigned char Data){
	 unsigned char i, ack_bit;
	 for(i=0;i<8;i++){
	 	SCL = 0;
		if ((Data & 0x80) == 0)
			SDA = 0;
		else
			SDA = 1;
		SCL = 1;
		Data<<=1;
	 }
	 SCL = 0;
	 ack_bit = SDA;
	 SCL = 1;
	 SCL = 0;
	 return !ack_bit;
}

unsigned char I2CRead(){
	unsigned char i, Data=0;
	for(i=0;i<8;i++){
		SCL = 0;
		SCL = 1;
		if(SDA)
			Data |=1;
		if(i<7)
			Data<<=1;
	}
	SCL = 0;
	SDA = 1;
	return Data;
}
		

Using the above implementation is really easy, next part uses an example of interfacing DS1307 with AT89C51 to read RTC registers (0x00 to 0x07).

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