>From: Martin Husemann <martin@laurin.teuto.de>
>Date: Thu, 27 Jul 1995 14:04:11 +0200 (MET DST)

>There are several kind of devices you can plug into such a port (maybe
>through some kind of cabling):
>
> - printers
> - PLIP cable (kind of a null-modem cable for parallel ports)
> - pocket ethernet adaptors
> - SCSI adaptors

FYI, There are also:

- audio devices (simple DACs, and something called the Portable*Sound
  Plus)
- MIDI adaptors

>Unfortunately, as the parallel port originaly was designed as a unidirectional
>device, all these devices use incompatible ways to transfer bytes. This makes
>things a bit more complicated than the serial ports, where line disciplines
>all use the same (hardware dependend) input/output routines and just decide
>what bytes to transfer.

IEEE standard 1284 (? not sure about exact #) defines an enhanced
parallel port with better support for bidirectionality, plus other
features.

>be a few shortcut macros for individual line disciplines (reading a 4
>bit nibble in the PLIP line discipline from the status port can be
>done with a single statement on i386 and pc532, but needs several
>statements when done bitwise with the generic interface).

Better to always return the nybble; the bits can be extracted as
necessary.
-- 
Mike Long <mike.long@analog.com>           http://www.shore.net/~mikel
VLSI Design Engineer         finger mikel@shore.net for PGP public key
Analog Devices, CPD Division          CCBF225E7D3F7ECB2C8F7ABB15D9BE7B
Norwood, MA 02062 USA                assert(*this!=opinionof(Analog));