AVR-Chat

>>> josecarlosfuentes@yahoo.com.ar 19/11/2004 12:49:38 am >>>
I want to use a Attiny11 (price under 0.54) and
implement a serial port.  Since it doesn't have a
USART I have to write the software to allow the
microcontroller to send and receive data.  If somebody
has done something like this in assembly or C please
let me know.  Attiny11 only has 1KB FLASH and 32
general purpose registers.
Thanks.
Jose


Here is some C code for a basic hard coded RS232 port.
A Delay() routine is required for the appropriate baud rate.

If this is for a production design then don't muck around with
calibrated RC timers and this software uarts, spend a few extra cents
and do it properly with a crystal controlled UART.


//***********************************************************
// Serial Port TX routine          
// A "bit banged" 8N1 serial port without using interrupts or timers
void Serial_TX(unsigned char b){
	unsigned char c;
	TXpinHIGH;
	TXpinLOW;					//start bit,
beginning of the transmission
	delay(bit_delay);
	for (c=0;c<8;c++){			//send each bit
		if ((b>>c)& 1) TXpinHIGH; else TXpinLOW;
		delay(bit_delay);	//delay for one bit	
	}
	TXpinHIGH;					//stop bit
	delay(bit_delay);   
	return;
}
 
//***********************************************************
// Serial Port RX routine          
// A "bit banged" 8N1 serial port without using interrupts or timers
unsigned char Serial_RX(void){
	unsigned char t;
	unsigned char c;
	unsigned char b;
	while(RXpin);				//wait for start bit,
beginning of the transmission	
	LEDon;						//Turn RED LED
on to indicate the RS232 transmission
	delay(bit_delay+(bit_delay/2));	//delay for 1.5 bits to put
sample in middle of bit
	t=0;						//assume
character is 0x00
	b=1;						//reset binary
bit counter
	for (c=0;c<8;c++){
		if (RXpin) t=t+b;
		delay(bit_delay);
		b=b*2;					//update binary
bit count
	}
	LEDoff;
	return(t);					//return the
received character
}