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'4X16 LCD (again)'
1999\05\14@230808 by jay

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Hi all,
I am trying to get an Optrex 4X16 LCD to work (HD44780) using the code from
Peter Ouwehand's home page.  The catch is I am using a 16C74A as opposed to
the 16C84.  Has anyone else tried this?  I turn the circuit on and the first
and third lines of the LCD are filled in with block characters, the second
and fourth lines are blank.  I am using the full 8-bit interfacing.
FRUSTRATION!!!!!!  Help me!! Help me!!!! I cannnnnn't seeeee!!!!!

Thanx in advance
Jay Mielke

1999\05\15@003506 by paulb

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Jay Mielke wrote:

> I am trying to get an Optrex 4X16 LCD to work (HD44780) using the code
> from Peter Ouwehand's home page.

 Ah yes.  I didn't have that filed under his name, but it is one of my
*major* references!

>  The catch is I am using a 16C74A as opposed to the 16C84.  Has anyone
> else tried this?

 Should work fine.  Minimal differences.

>  I turn the circuit on and the first and third lines of the LCD are
> filled in with block characters, the second and fourth lines are
> blank.  I am using the full 8-bit interfacing.

 The display uses "two-line" mode.  The "second" line is as you have
found, actually the second and fourth lines.  Looking for "Function Set"
in http://www.iaehv.nl/users/pouweha/lcd0.htm#instruction_set you will
note that you have to set up bit 3 ("N") as a "1".  For you, the command
value will be $38 or $3B.

 He appears to have fixed the typo I reported.  Good ;-)

 Note the display addresses of the four lines.  They are tabulated in
http://www.iaehv.nl/users/pouweha/lcd.htm which *also* reminds you of
the correct value for "N".  The first line scrolls automatically to the
third, and the second to the fourth.
--
 Cheers,
       Paul B.

1999\05\15@005823 by paulb

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Jay Mielke wrote:

> I am trying to get an Optrex 4X16 LCD to work (HD44780) using the code
> from Peter Ouwehand's home page.

 Something worries me however.  Marc Simons' example of interfacing
( http://www.iaehv.nl/users/pouweha/lcd_examp.htm ), though it *will
work*, is IM(NS)HO rather kludgy.

 R1, C5, T1 and R2 make the code time-critical and are entirely
unnecessary.  RS should instead be commoned either *directly* to the Clk
pin 3, or to D (Data) on the 4092.  The code must be adjusted to suit,
but is actually simpler and ... faster!

 Now, you do need to delay to permit the HD44780 to do its job, but in
general if you use concise code to load the commands/ data, you can
then perform other tasks whilst waiting.

 Also, pin 1 of the 4092 (Strobe) might as well be tied high instead of
to the EN.  The circuit certainly works as posted because the HD44780
latches the data on the trailing edge of EN, so the latch function is
entirely superfluous.
--
 Cheers,
       Paul B.

1999\05\15@024117 by ns

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I haven't read the code but if it was meant for the '84 and uses 8 bit
data bus, PORTA was probably used for control lines.

Remember on '74 that PORTA has analogue to digital converters which
defualt to analogue mode on power up.  You have to set them digital mode.
That's what I would check.

On Fri, 14 May 1999, Jay Mielke wrote:

{Quote hidden}

1999\05\15@031106 by Lynx {Glenn Jones}

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What i did to debug my LCD troubles was make a delay routine of about a
second or two, then call it each time the enable line changes state, so i
could use a logic probe to diagnose things.

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On Fri, 14 May 1999, Jay Mielke wrote:

{Quote hidden}

1999\05\16@105027 by Wagner Lipnharski

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When you apply power to pins 1 + 2, polarization voltage to pin 3 on a
4xN LCD, the first and third lines comes up in black characters since it
is "power up preset" to one line mode, so the first line is on (remember
that the first line is broke in two and it extends as the "third"
line).  If your PIC can't change that, it means that your device is
unable to reprogram the unit to 2 lines.  If you don't have an
osciloscope to debug it, just insert delays of 1 minute or more between
data sent to the LCD, so you could measure the state of the lines using
a simple voltmeter.  Just measure all the 14 lines after each change,
make a map and compare to what it should be.

Wagner Lipnharski

1999\05\16@160543 by Eric Oliver

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Where ya been, Wagner ?


On Sunday, May 16, 1999 9:49 AM, Wagner Lipnharski [SMTP:spam_OUTwagnerlTakeThisOuTspamEARTHLINK.NET]
wrote:
{Quote hidden}

1999\05\17@111914 by Kellar Kevin K CNIN

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I have a project which also uses the 16c74a.  Sometimes I have the same
problem with lines 1 and 3; however, it is caused because I forget to turn
off my debug switch.  This switch comments out a power up delay for the LCD.
( I do this for simulation) So my first comment is confirm that your power
up delay is long enough.  I also experienced the problem when I replaced one
brand of LCD with another.  I had to insert a small delay in my busy flag
routine. (I monitor the busy flag pin14 for completion of the command)  I do
not know for sure why I had to do this, but it works now.
Good Luck
Kevin

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