Graphics Reference
In-Depth Information
Fig. 1.11
The layout of the first-generation Xerox optical mouse chip, which I did quickly toward
the end of 1980, had the lateral inhibition, done-detection, and image storage logic distributed in the
pixel cell array, along with image cross-correlation logic. The arrays at the bottom were essentially
programmed logic arrays (PLAs), programmed as the timing generator, the counters, and the logic
that converted the sensed move directions, or image cross-correlations, to counter increments. Six
of the bond pads are cross-coupled inverter pairs, to debounce the SPDT switch contacts of the
three mouse buttons. Of the eleven output pads, four are for the motion encoding and seven are for
observing internal timing signals
done-detection logic waits to see when it has committed, but this strategy only works
if the metastable states are static, not oscillatory.
Oscillatory metastable states were well known to us in the 1970s, having been
reported by Chaney and Molnar [
7
], who showed the oscillatory metastable behavior
of a pair of cross-coupled TTL logic gates; Fig.
1.12
shows random samples of a
flip-flop output being put into and exiting its metastable state. Charlie Molnar had
worked with us at Caltech during the early VLSI developments, and was influential in
