🚀 go-pugleaf

Is it true that the 68HC11 EVB comes with a 68681 or a 2681 DUART onboard?

I have one of the smaller EVBUs and I attached a 68681 to the bus in 
expanded mode. I can write to it fine, even though the DTACK line never
goes low. I cannot read from it all. 

I am concerned because quite a bit of the bus timing of the DUART
seems to be dependent on the X1 input, to which I have attached to a
271ns crystal as recommended. The CS line as decoded from the HC11 is
only 300ns long.  Is is possible that the bus cycle of the HC11 is too
fast for the 68681?  

If there is one on the EVB, would anyone be willing to fax me a copy of
the schematic? I've been poking around for some time with no success,
so even an assurance that the DUART can keep up with such a slow bus
cycle would be helpful.  

The data sheet claims that the maximum time from CS going low to 
data being asserted on the bus is 175ns, but this also seems to be
a factor of the phase of the X1 clock. 

thanx

Eric Hoffman
hoffman@cmf.nrl.navy.mil
(202) 767-1683 fax