20 Apr
2025
20 Apr
'25
1:58 p.m.
On Sun, Apr 20, 2025 at 12:36 PM Steve Lewis via cctalk
<cctalk(a)classiccmp.org> wrote:
Anyway, just poking around, no specific question here
:) Wel, except a
related/unrelated question -- why does MIDI use 5mA current loop?
I suspect one reason is that the current loop input can easily be
opto-isolated which will avoid ground loop problems.
And is
that why MIDI adopted the joystick port? (IBM original joystick card spec,
didn't it involve measuring electrical discharge? so it is effectively a
current-loop port? is that somewhat accurate?)
MIDI doesn't use the joystick port. By that I mean you can't use an
original IBM Game Control Adapter (or a clone of it) for MIDI
But many older soundcards included a joystick interface (one main use
of a soundcard back then was games). And to save connectors/space on
the bracket, the MIDI interface was carried over some pins of the same
DA15 (probably by only allowing one joystick, the orignal IBM adapter
allowed for 2)
-tony