Google bit bang uart 8051 and you'll find what you need to no bit bang uart 8051 - Google Search
If it a 40 pin dip it should have uart on pin P3.0 and P3.1 If so look here **broken link removed** I have a book in my truck on how to do uart and a lot more they use a lot of them at the plant I worked at but i never programmed one just fixed motor controls h-bridges and sensors. Here if any one wants to read the datasheet http://www.datasheetcatalog.com/datasheets_pdf/8/0/5/1/8051.shtml
that is very simple
you just need to copy the data in SBUF register, it means Serial communication buffer register.
command would be:
MOV SBUF,#01H
here 01H is the data to be transmitted
but u need to set few SFR before that
those are SCON, SMOD, TMOD and TCON
also you need to load TH1 and TL1