Bob Drzyzgula wrote:

> Could this then be rephrased "the current sourcing capacity of this
> parallel port is limited by the current sourcing capacity of the ISA
> bus"?  And if so, what is the +5V capacity of a typical ISA bus?

  No, it couldn't (be thus rephrased).  The ISA bus is irrelevant to the
discussion.  Its capacity to deliver +5V is about 1 to 2 amps
continuous, similar for +12V, about ¸ amp each for -12V and -5V.

  This is unrelated to the parallel port which might just as well be
included on the motherboard (usually is nowadays) or a PCI card.  What
limits the parallel port is the chip attached, probably the most current
available from discrete TTL, less from the 82C11 series chips and least
from the multi-I/O and EPP/ ECP chips.

  The possibility of the current dropping off by virtue of certain
output configurations however, and brownouts muddling the PIC (remember
the thread?) is, at least to me, however off-putting.

  The keyboard conenctor is capable of an amp or so, but this involves
mucking about with unwieldy "T"-adaptors (called "wedges") and risks
upsetting the keyboard on this account.

  The Game port however, is a particularly serviceable means of sourcing
+5V as well as four direct inputs to the PC and one output.  There is of
course a tendency to leave it off recent PCs (well, how many people want
to use their PCs to play games?), mostly on the presumption that it is
now part of the sound card.  Ergo, current A-I-O boards usually *do*
have it as part of the sound card emulation.

http://www.hut.fi/Misc/Electronics/pc/interface.html

http://www.blackdown.org/~hwb/hwb.html mirrored at:
http://www.sonic.net/~alanwall/hwb/hwb.html
-- 
  Cheers,
        Paul B.