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'LCD drive with 16C65A'
1998\10\26@092636 by rvfintel

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Hello

Has anybody tried driving LCD displays with the PIC 16C65 A.
In particular, I would like to drive single digits as it were.

Thanks
Rudi

1998\10\27@162518 by Russell McMahon

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I haven't tried it but its not conceptually difficult.
If want to drive a single digit you have enough pins to drive the
segments directly.
Requirements are:
1. You must provide a backplane signal.
2. The backplane must be a "rail to rail" square wave signal with a
50/50 mark-space ration (high/low).
3 "Lit" segments are of opposite polarity to the backplane signal (on
when off, off when on).
4. 'Unlit" segments are of the same polarity as the backplane signal
(on when on, off when off).

The average signal sent to a lit segment MUST be zero -e the duty
cycle MUST be EXACTLY 50% long term. If it's not you get a DC
component and the LCD will die in time.

If you want to drive more segments than you have pins you can
multiplex as long as the above rules are met. This can get fun with a
raw PIC as driver. About then it is probably better to either use a
cpu with inbuilt LCD drive or use a specialised LCD driver chip or
use one of the many self contained LCD displays.

If you want to drive separate digits you could consider chips like
the MM5453 (an oldie but still useful)(40 pin DIP is most common
form). These only take 2 pins to drive (data and clock). I have PIC
code available if desired (this is written in PICBASIC but could
easily enough be converted to assembler or C). The MM5453 drives
about 32 segments as I recall.

Rudi wrote:


>Has anybody tried driving LCD displays with the PIC 16C65 A.
>In particular, I would like to drive single digits as it were.

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