Hello Paul,

A good site about smart cards with schematic and software can be found at http://www.elecdesign.com/Articles/.../6412.html

Source code can be seen at these addresses http://www.elecdesign.com/Files/29/...ure_04.gif
listing 1 of 2
http://www.elecdesign.com/Files/29/...ure_05.gif
listing 2 of 2

It performs the following
A simple example of such an application program.

Send a valid "answer to reset" response each time the ISO2 contact is activated;
wait for the presentation of a PIN (5678h) at the address 1234h;
answer 8765h (only once)! When exactly 2 bytes are read from address 4321h;
lock the card until the next reset.

It should be easy to convert the software to 80C51.

I hope this helps.

Regards,

Charles Bannister