AVR-Chat

At 08:49 AM 11/18/2004, Jose Fuentes wrote:


>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.

You may be a bit hosed here.
The T11's RC osc isn't calibrated, so you'd have to use a resonator or xtal 
at the cost of two pins.   If that works for you, then set up an int at the 
baud rate.

Receive:
Put RXD on the hardware int pin (PB1)
When you see the start bit, set the timer to int you in half a bit time.
When that int fires, sample the data. If still low, you have a valid start 
bit, and the next 8 timer ints simply sample and shift.
If you want, you can pay attention to the stop bit, one more int, should be 
"idle".

Transmit:
TXD on any pin.
Set the int to fire at the baud rate.
Send a start bit, 8 data, and one stop..


It's not that awful, but that means you have only two more pins available 
on the chip, and one of them is reset..

8 pin chip, VCC, Gnd, X1, X2, TXD, RXD, Reset..  One pin left.

Don't spend it all in one place!