The method shown in AN563 could be expanded to drive 3 or 4 commons.
     This method is using what is called 1/2 bias.  Three commons would
     require 1/3 multiplex.  If you get a copy of some documentation that
     shows the waveforms for 1/3 mux, with 1/2 bias, the required code
     should be easy to modify from the ANote.  My personal favorite LCD
     info is in Hitachi's "LCD Controller/Driver LSI Data Book"

     Naturally, the delays involved in setting the waveforms will induce
     more DC into the LCD.  To minimize this, run as fast as you can and
     write all ports in a burst of code that changes all ports together as
     fast as possible.

     Rgds, Brian.


______________________________ Reply Separator _________________________________
Subject: PIC as muxed LCD driver
Author:  Gregg Blas <greggwb@NETCOM.NETCOM.COM> at Internet_Exchange
Date:    11/20/95 10:05 PM


I've only been reading this list for a month or so,
and already picked up numerous pieces of interesting
information. I am also new to the PIC processor, and
am about to start a new project using the 16C65 and
would appreciate any assistance on the following problem:
  Microchips' Ap Note AN563 gives some pretty specific
info for the hardware and software for using a PIC as
a multiplexed LCD driver directly from the pins, but the
example is for a simple 2-backplane LCD. I would like
to use the same technique to drive a 3-backplane LCD...
basically a 3 3/4 BCD digit LCD with a few annunciators.
Is such a thing possible without violating the DC voltage
spec of the LCD? How complex is the code, and can it be
done with a '65?  Any code examples would be appreciated...
TIA
greggwb@netcom.com
          Gregg Blas
 -- greggwb@netcom.com --