TU-58 rollers and emulation (was Re: VAX 11/725)

From: ajp166 <ajp166_at_bellatlantic.net>
Date: Sat Mar 24 12:22:48 2001

From: Clint Wolff (VAX collector) <vaxman_at_qwest.net>
>I've written one for DOS that needs some tweaking still... I'll cut
>loose the source code if someone wants to fix it up. Basically, it
>sometimes gets out of sync and you have to power down the 750 and
>restart the PC to get it back working...


You need to acknowledge that INIT from the host (750 or pdp11)
can force the tu-58 back to initial status. on the real tu58 thats a
break char and the resulting Framing Error from the Uart causes
a TRAP interrupt (higest priority nonmaskable interrupt) on the 8085.
A PC would have to sense a Framing Error (Character with no stop bit
for at lest two character times) and force the code back to the
starting point where RSP is restarted.

I have prints and manuals plus some of the designers notes from by days
as a Digit. Back when they were easy to find and a cheap way to put
512k of block oriented storage on a serial port of PDP-11 systems.

I also have a few that used a parallel IO (used only for PDT11/130) that
are otherwise identical.

>THANKS Allison! I bought two from Keyways, Inc. for $40 + shipping...
>For that price, I could have bought 20' of Tygon tubing... Live and
>learn...


For 40$ that should have been 80ft of tygon and at roughly .300 inches
of it per roller that would be enough for a couple of Sagans of them.

  <one Sagan = billions and billions)

I had it handy and it works *ok*. It's weakness is that it dents if the
cart
is left in place for long periods. It recovers if shape if the cart is
removed
but a more resilient material might be better. I used tygon as I had it
at hand. A rubber hose material with the right dimensions would be a
good choice. Also the dimater for the TU58 roller is non critical save
for it works best if round. ;) The actual tape speed is controlled
by the cpu and a PLL circuit and has a +-10% or more tolerence of
roller diameter before there may be a tape speed problem at the ends
of the tape.

Allison
Received on Sat Mar 24 2001 - 12:22:48 GMT