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

From: Clint Wolff (VAX collector) &lt;vaxman(a)qwest.net&gt; 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. 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