smart card read using avr
You need to know the protocol for the paticular type of card you are communicating with.
Some cheap cards use a synchronous interface with an external clock to transfer one bit at a time.
The majority of cards use 9600baud rsr232-style signalling with 0v/5V logic levels. The data is half duplex on one connection so you have to tristate your data output when you are not sending bytes.
After the ATR (answer to reset) the protocol is set by the card manufacturer or programmer.