Do you want to convert it in your code (for 8051)?

If so , you will have to understand 26 bit wiegand format, and then extract the information in your code, and then convert to RS-232 using on board serial port.
www.keyless.com/PDF/26BitWiegand.pdf

If you need a wiegand reader with RS-232 output, try this

http://www.internationalbarcode.com/701.htm

I would suggest you to try a little search using a serach engine, before submitting a post, and asking people to do that for you.

Don't mind.

Regards

IA