unibus to modern disk interface?

On Oct 14, 2012, at 9:40 PM, Eric Smith wrote: Qbus is at least a little more forgiving (10uA max at low level seems a bit odd for TTL, given that it's lower than Iih); drivers have a max leakage of 25uA at 3.8v, while receivers have a max leakage of 80uA over their input range. That's not impossible to achieve with some discrete transistors; a 2N4401 fits the bill nicely for the output stage (and meets the rise/fall time constraint). I'd be more inclined to use a FET input stage or possibly even a comparator to achieve the desired hysteresis and threshold voltage, though a) I haven't thought about what the impedance effects of the positive feedback would be, b) I've had a hard time finding good comparators that work in the correct range and have a short enough propagation delay, and c) a Schmitt trigger made with discretes is probably a good enough solution. I'd love to continue this discussion on or off the list if anyone is seriously interested in developing new Unibus/Qbus boards. A standard solution that is easily reproducible would help quite a few people, I think. - Dave