It will be surprising to see many a debouncing idea presented in books on digital circuits exactly the way it has been drawn by Michael.
and the switch as input to a 8255.

Many "books" are written to achieve fame or gain for the author and as opposed to an entry in a forum, there is no one to argue the alternatives/mistakes. Just blindly taking what is written in a "book" as gospel truth is a very common mistake, I remember once using a book on the ISA interface and I made a wonderful design that did not fit because the dimension drawing of the card was wrong in the book.

Much more trust can be put into internet publications from the manufactureres - at least later editions - since every mistake result in a barrage of e-mails and just to avoid the mail getting overloaded they usually correct the mistakes quite rapidly.

One amazing exception is "the bible" even my original print version is error free. Now comes the catch: even this error free publication is not correct for some modern derivatives and must thus be taken with a grain of salt as well.

Erik