... with the caveat, that you must first read and understand the datasheet for each and every component you use, including the PC parallel port.

You'll be disappointed to find that the '51 doesn't really have a tristate mode, per se, but go ahead and read the datasheet (AKA "the bible") anyway.

If you're interested in reducing your workload, you might want to read the numerous pages on the www that focus on the PC parallel port in EPP mode.

Since the very early '90's, that mode has been supported via BIOS provisions in nearly every new PC. The PC hardware provides you with the ability to write code on your PC that writes to the parallel port in LONG WORDS, yet multiplexes the data out for you in bytes. It provides steering logic for you, by means of which you can easily detect whether the information is data or control. EPP provides you with a nWAIT/RDY signal that tells you when the transaction is complete, which simplifies timing issues. EPP mode is bidirectional. It works essentially the same, regardless of the direction in which use it.

Don't confuse the very simple EPP with the much more laborious, and therefore, necessarily very slow, SPP or incredibly complex ECP, the latter being intended for complex printers.

There's nothing, BTW, to prevent you from using presettable counters rather than latches to store the data you intend to use as addresses. That will save you some time and effort in the code as well.

RE