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controlling GPIOs from DOS (Announce)

posted by bretjohn Homepage E-mail, Rio Rancho, NM, 05.12.2013, 16:28

The first parallel ports IBM came out with were bidirectional, and then they made them unidirectional (they were a little cheaper to make that way), and then with the PS2's they made them bidirectional again (and they weren't even EPP or ECP, they were just bidirectional). You don't actually need EPP or ECP to have a bidirectional port.

Making a port EPP, ECP, or regular/bidirectional is usually something you can change in the BIOS.

The problem with anything other than nibble mode is that both devices (the computer and the end device, usually a printer) have to be configured exactly the same way. If it's a one-off application, or has a very limited, controlled distribution, that's OK since you can manage everybody's configuration. If it's a general-purpose application intended for wide distribution, it's much more problematic.

Nibble mode doesn't have that problem -- it always works no matter how things are configured. But, it's slower -- at least in theory, it should only be about 1/2 as slow, though in actual practice I'm not sure how fast it really is. They claim parallel ports can reach speed of 12~16 Mbps, so I would think even in nibble mode you should be able to get at least 1 Mbps.

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