18 Oct
2007
18 Oct
'07
12:52 p.m.
I suppose in the PC (as in IBM-compatible) world
things tended to get their
own ISA card (if they couldn't be driven via RS-232). IBM really missed a
trick in not making the PC's parallel port bidirectional from the start. :-(
THey almost did, and then didn't enable it, or document it!. Look at an
original PC printer port card. There are 3 pads at 0.1" spacing, the
middle one of which goes to the OE/ pin of the '374 (data output latch),
onf of the end ones is groud, the other end one is the unused output of
the '174 (control output port). The frist 2 are linked by a trace. Cut
that last trace, solder in a 0.1" pin header and use one of those
well-known jumper links to sleect whether you want a bidirectional port
or not.
This is _not_ shown in the Techred for some unknown reason....
Of coruse it's not as versatile as the BBC user port, which let you set
the driection of each pin individually.
-tony