Unibus / Qbus bus drivers and receivers - test-drb@ccmp.vtda.org

29 Jun 2001

From: Chuck McManis &lt;cmcmanis(a)mcmanis.com&gt;

...
 At 09:30 PM 6/28/01 -0700, you wrote:
 Well, the question is "how worried about
ringing *should* I be in a
single backplane configuration if I use bus drivers which have a
rise/fall time of 9 ns, when the bus spec says that the rise/fall
time of bus drivers must not be *less* than 10 ns?"

I'm guessing that it will probably be OK, but I really want this
thing to "work first time" and be reliable so I feel a little
uncomfortable cutting corners like this right at the outset. 
I take it you are worried about violating the AC spec that reads in part:

Generally speaking Qbus is very robust and the design rules are not
easily broken nor the bus.  Standard devices like LS244 and LS245s
work quite fine from expereince.  Stick with 74LS or 74L if you have
them or can find them.   CMOS in the 74HC, HCT and friends
however are a bad choice for interfacing the bus, though they may be
acceptable in down stream logic.

Remember the bus is terminated to avoid pain.

Allison