Score: -2 (-1 Message Not Useful, -1 Offensive/Flame)
Lisa.
Did you get it in an Antoque shop?

Evidently I need to elaborate

Lisa, please give this to your teacher

Dear Sir/Madam:

In the olden days when the king of diamonda were still a jack, there were few to none chips made for interfacing the '51 to the outside world. At that time we kluged the 8255 (which is made to match the x86 uCs and a lousy match for the '51) into our designs because no better solution was available. Today, no, for at least 5 years many better solutions has arrived. First there was the PSD chips from the WSI (now ST micro) which effectively provided a 8255 equivalent tailored to the '51. Later the CPLDs came down in price to become a feasible alternative. Today, with internal Flash and RAM being the norm, you can have up to 64 I/O pins on a 'regular priced' '51 derivative, which in almost all cases, eliminate the need for external I/O solutions.

Anyhow, should I hire one of your graduates and that person include a 8255 in a design that person will be unemployed 10 minutes later. I consider it a great disservice of you to your students to teach them such an outdated design methodology.

Respectfully yours

Erik Malund