I am currently working on a redesign of a battery operated product that uses
a 28 segment LCD display. Since the production volume is going to be
substantial (>10K pieces) I am rationalizing the hardware to its bare bones.

I want to eliminate the current 32 segment LCD driver chip (a Motorola part)
and do the multiplexing with the PIC itself. One way to reduce complexity is
to multiplex the 28 segments as 7 segments X 4 colums. Not being familiar
with LCD Multiplexing, I checked out the Intersil databook (yes, taken over
by Harris awhile back) to see how their LCD Multiplexors worked. They use
something called tri-plexing, which calls for each row and column line to be
able to source 4 discrete voltages - not an easy task with a PIC.

What I'd like to ask is this: Does an individual LCD segment act like a
capacitor in that a stored charge is proportional to contrast, or is it
simply that applying a potential difference across the segment causes
crystal twist and the effect's duration and intensity is entirely physical?

OK, the reason for this complicated question is this: I can setup a 28
segment LCD display as a 7X4 array. All 7+4=11 lines would be tristatable so
that only one of 4 column lines would be active at a time, and an AC signal
will be applyed across the 'ON' segments by alternatively sourcing and then
sinking the appropriate segments. A segment line (1 of 7) would be tristate
when the driven segment is 'OFF'. This is to prevent other segments
receiving 1/2V while they are connected as 2 segments, in series, with the
center connected to a tristated column driver. By only sourcing segments on
one pass, and then sinking on the next, we prevent 'bleeding'.

However, if an LCD segment needs a sustained charge to stay twisted, then I
would be concerned that any leakage off of segement charge would kill the
display's contrast.

As well, since tristated lines are used, how sensitive would the display be
to leakage current overall?

I know this is somewhat obscure. Perhaps someone has already tried this or
done the research.

Thanks.
Regards, Dana Frank Raymond
dfr@icom.ca