I2C (TWI) ACK flag register use

[Lauris]

Hello eeryone,

one question apeared while trying to make full I2C(TWI) interupt based driver. main problem is after transmitting nACK when I can set it back inside ISR(); and don't leave I2C hanging with nACK in register that way uC being isolated from i2C line.

    case 0x40:	//SLA+R has been transmitted, ACK has been received
	  if (cnt_R >= TWI_rcv_sz)
	    TWCR &= ~(1 << 6);		//transmit nACK to inform about last receiving byte
	  TWCR |= (1 << 7);		//Eanble TWI, to continue transmition
	  if (TWCR & (1 << 6))
	    TWCR |= (1 << 6);	//reseting TWEA back to ACK
	  break;

would it make sence what I wrote ahead that nACK writed to registers, transfer started and after that swiching nACK flag back to ACK - sill nACK would be transfered? if not then how to do that inside interupt function. Any ideas?

P.S. this case is writed for Atmega8

Laurynas.

 

[Kurenai_ryu]

as far as i remember, if you send a NAK (via clearing TWEA) you only need to restore TWEA when you receive the STOP condition (0xA0 i think) and make sure that TWI is cleared ONLY at the end of your ISR.