3 Jan
2010
3 Jan
'10
2:25 p.m.
On 3 Jan 2010 at 17:46, Tony Duell wrote:
No it's not.
As an aside, I have a machine using standed
'360K' 5.25" drives --
that is Tandon TM100s -- which does correclty implent a disk-changed
feature. How it does it is to have the 2 drives separately cabled to
the controller board and the drives always selected. It then looks for
a change-of-state of the write-protect line. This must change if a
disk is inserted or removed.
Anyone want to guess the machine? I have 3 of them, all different
models (one only has on disk drive).
Heh, nihil sub sole novum.
I implemented that on the Durango F85 in 1979, but I don't think
that's the machine you mean. We had a terrible problem with customers simply changing diskettes whenever they
wanted. The drives
were cabled normally, just selected and the status of the write-
protect line checked every few hundred milliseconds. The FDC was a
WD1781, so WP status was available all of the time, regardless of the
state of the motor. The drives were TM-1004Ms or Micropolis 1610s.
The machine I am thinking of uses a WD1793 or similar. The write-protect
checking is done in hardware -- as I said both drives have separate
cables back to the contrtoller PCB. The MX jumpers are fitted on the
drives, causing them to drive the cable all the time, so the WP signal is
always valid from the drive. There's a littlebit of locking involving a
flip-flop,. etc that detects if the WP line changes state. (I would have
to grab the schematics, it may be it only detects if the WP line goes to
the asseted state, not the revers trasnition. That's certain to occur
when a disk is inserted anyway).
One problem we never did solve was that of the
customer powering the
machine down, without exiting an application. But that persisted on
all systems until someone invented the "soft power" button.
YEs. Another of my machines (an early form of 'unix for the masses' -- it
has a graphical front end over Uniplus+, but you tend to end up in the
shell anyway -- has a touch switch to turn the power on and off For power
down, the service processor detects the touch on the switch and then
tells the main processor to flush the caches, etc before turning off the
main power relay.
The identity of the machines/ The first (WP used for disk change) is the
HP9826 or HP9836, the latter is the Torch XXX (I think the Whtiechapel
MG1 does something similar too).
-tony