Hello all,

I'm trying to rewrite I2C routines in C from assembly to practice C programming, I run into a problem and I'm having hardtime to figure out how to write these instructions RL, RLC in C. So far Start, Stop, Write, Repeat Start routines are working, but the Read routine doesn't work. (Received data is not correct as reading variable Data. I'm using Ceibo emulator and Keil IDE. However data that is displayed on oscilloscope is correct). So I think that there is something wrong with the way I manipulate data in the routine. Here is what I did:

unsigned char I2C_Read (unsigned char Data)
{
	unsigned char Bit_Cnt;
	
	Data = 0x00;

	for (Bit_Cnt = 0; Bit_Cnt < 8; Bit_Cnt++)
	{
		Data |= I2DAT;
	
	// Receive MSB first
	
		Data = Data << 1 ;

	// Rotate left

		while (!ATN){}

	// Pool ATN flag

		if (!DRDY)
		{
			Fault = 1;
			break;
		}

	}

	Data |= I2CON << 8;

	// Get last bit in the I2CON reg 
 
	I2DAT = 0x80;

	// Send Ack bit

	while (!ATN){}

	if (!DRDY)
	{
		Fault = 1;

	}
	return (Data);
}

Here is the assembly routine that works

R_Loop:	mov BitCnt,#08h			; Set BitCnt = 8 (receive 1 Byte at a time)
RBit:	orl A,I2DAT			; Read I2DAT.Get 1st bit (MSB). Clear DRDY
	rl A				; Shift left received data
	jnb ATN,$			; Wait for new data
	jnb DRDY,RDErr			; Wait for DRDY = 1 (Detect rising edge of SCL)
	djnz BitCnt,RBit		; Loop until the last bit
	jnb ATN,$			;	
	mov C,RDAT			; Read last bit from I2CON register
	rlc A				; Get full data byte

Any inputs would be greatly appreciated. Have a great day.

Best Regards,
T.L

PS: My MCU is 87C752