"Terry Vernon" bravely wrote to "Ken Hrynchuk" (27 Sep
04  21:44:00)
 --- on the heady topic of "8-bit LPT cable"

 KH>  KH> Has anyone done 8-bit file transfers via the PC's parallel port?

 KH>  TV> Once did it regularly, using a systen called (IIRC) LapLink.
 KH>  TV> The program came with a fancy cable with both parallel and serial
 KH>  TV> connectors - I MAY even have one of those aruund here somewhere!

 KH> Thanks, Terry; I've read conflicting reports re: Laplink being 8-bit.
 KH> Perhaps some versions were 4-bit only? Do you remember running across
 KH> any cable documentation in Laplink's docs?

 TV> Sorry, don't have the docs anymore.

 TV> PC printer ports always had 8 data lines, so why would it have been
 TV> only 4-bit?.   Did some implementations have only 4 input lines?

The original IBM PC printer port was single direction "output" only.
Some second party realized that the handshake signals however had both
input and output lines. They then proceeded to kludge them as a
bi-directional I/O but there were only enough input lines for 4 bits.

The interesting bit about the original IBM PC printer port was that
the I/O chip was a 74LS373 (4) octal buffer, a bi-directional IC. It
was originally hardwired for output only by grounding the direction
pin 1. Many people noticed that all which was required to make the
port bidirectional was to wire this pin 1 to a spare bit in the
control port to make the direction bit available in software, via its
hex latch (74LS244) spare pin 15. Later bidirectional parallel ports
did just that. The story goes that the IBM folks had initially
intended making the printer port a parallel port but changed their
minds before releasing the IBM PC. I even had an old printer card with
a jumper to enable it (but hardwired for output only too!).

M*i*k*e

... I'm_ a Fidonut and I'm_ o_k_.  I FREQ_ all_ night_ and I flame_ all_ day
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