hi, i dont know what is your project actually. and i think that it would be an alphabet that should be shown on 7 segment.
so here is what i suggest.
you should send three letters one by one from your computer to microcontroller. and ask your microcontroller to recognise them and show them on 7 segment.
you can send characters from your computer using hyperterminal. (builtin the windows xp version. and if you are using windows 7 you have to download it from internet)
here. you will use serial cable connecting your computer DB9 PORT with SERIAL port of your circuit board. this connector connects to max232 IC. this ic is used for serial communication. purpose. because, the serial data is at 9v and controller needs 5v. so simply it can be thought of as a voltage level converter. now the controller recognises the character. and show it on 7 segment.
HOW CONTROLLER RECOGNISE IT?
every letter has its ASCII code. this code has to be stored in your controller. now you can compare them in your code.
all the best of luck
- - - Updated - - -
i can give you some algorithm design:
>>>>
while(wait for data to come on serial comm port) OR use serial communication interrupt if your controller supports this.
void function_of_serial_comm()
{
if (data==a)
show a on 7 segment
else if(data==b)
show b on 7 segment
AND
SO
ON......
}