Typically LCDs are operated using the 4 bit interface to save pins.
However, most modern LCDs don't need any initialization if you are using
8 bits.  Simply put the character on the data lines and toggle the
enable line.  For four bits you do need to go through some convoluted
initialization.

The LCD has the ability to tell you when it is done, but most folks tie
the R/W line low and simply wait long enough.  The mistake most people
then make is not waiting long enough.  The LCD will only go so fast, but
it can go as slow as you want.

There used to be some pretty good stuff on the Internet about LCDs, but
most of that is pretty old now.  It is a pretty simple problem.

I've never been that thrilled with the Microchip libraries, especially
for 8 bit.  Usually it is a lot simpler just to do it yourself, although
for an LCD, I'm sure there are plenty of good libraries out there.
Beware, though.  There is a wide difference in speed between different
LCDs.  If you have code written against the HD44780 datasheet it ought
to work with pretty much any LCD.  But code someone wrote for some
random LCD might not work with the one you happen to have.

Also, some LCDs have some extra features that aren't in the HD44780.  A
library written against these can cause confusing results. I was
surprised to find some of these in the LCD on my Explorer 16.  Microchip
apparently uses a number of different displays on this board, but the
one I have has multiple addresses for some positions on the display.
This can actually be convenient sometimes, but can also be a real pain.

So I would suggest get the HD44780 datasheet, do what it says, but start
out real slow.  Once you get things working, then adjust to the times in
the datasheet.  It isn't a very hard problem, and over the longer term,
you will be better off understanding what you have.

You can probably learn a lot from other people's code.  I wouldn't put
too much time into Microchip's, tho.  Their code tends to be
conditionalized for a number of PICs and demo boards, and wading through
all the #ifdef's can be a real challenge.

--McD



On Tue, 2015-03-17 at 12:09 +0000, Matt Rhys-Roberts wrote:
> Hi, I'm right at the start of trying to drive a generic ST7066U-based=20
> 2x16 LCD character display, compatible with HD44780/KS0066/KS0070B etc.
>=20
> Talking to the display can be done using 4 or 8 bits. I'm using 8 bits=20
> for now until I can prove any advantage to using 4. Pin count costs,=20
> perhaps? Any opinions on this please?
>=20
> It seems logical to use the pre-written LCD library code provided by=20
> Microchip, rather than write my own, at this stage. So I think I need to=
=20
> include xlcd.h, but then I'm not too clear about getting the job done. I=
=20
> can see a number of .c files under=20
> /opt/microchip/xc8/v1.33/sources/pic18/plib/XLCD which I guess I'd call,=
=20
> and pass parameters accordingly.
>=20
> So my question is, has anyone seen a good user guide to setting all this=
=20
> up? I seem to have found the details before finding any kind of manual.
>=20
> Many thanks,
> Matt.


--=20
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