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'initializing a 2x8 lcd'
1996\12\17@142542 by Tony Matthews

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Hello
I am having trouble initializing my 2x8 optrex lcd w/hd44780a
controller
in 4 bit mode.I have tried everything I could glean from the FAQ's but
it just
does'nt shift to 4 bit mode and all subsequent writes cause the cursor
to move
two places.In the simulator the write routine 4 bit writes upper
nybble,lower
nybble with no extra loops and the character printed bears no relation
to the
one I was attempting.I am using bits <4..7>b for data & bits <1..3>b for
control
The rs & r/w bits are output with enable low then enable is toggled high
and the
4 data bits are output then the enable bit is toggled low.
       Thanks in advance for any help. Tony M.
ps Digi_Key #73-1106-nd

1996\12\17@172212 by Kalle Pihlajasaari

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Hi Tony,

>  I am having trouble initializing my 2x8 optrex lcd w/hd44780a
> controller
> in 4 bit mode.I have tried everything I could glean from the FAQ's but
> it just
> does'nt shift to 4 bit mode and all subsequent writes cause the cursor
> to move
> two places.In the simulator the write routine 4 bit writes upper
> nybble,lower
> nybble with no extra loops and the character printed bears no relation
> to the
> one I was attempting.I am using bits <4..7>b for data & bits <1..3>b for
> control
> The rs & r/w bits are output with enable low then enable is toggled high
> and the
> 4 data bits are output then the enable bit is toggled low.

You might have a look at the following I did in Pascal just
to get an idea of the steps to take.  The plan is to write
the reset to 8 bit mode comand to the display 3 times as
recommended in the data sheets and then send the set to
4 bit mode command once.  All 4 of the above were single byte writes
after the last one then you start to write nibble/nibble.

http://www.ip.co.za/people/kalle/project.htm#lcd

Cheers     *<<<-|
--
Kalle Pihlajasaari   spam_OUTkalleTakeThisOuTspamip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

1996\12\17@212026 by Tony Matthews

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Kalle Pihlajasaari wrote:
{Quote hidden}

Thanks I'll go and look.I did write my code just as you say like the
FAQ's I read
indicated I should. Plus a few variations.Is it necessary to pull the
unused inputs
to the lcd low externally ?
> http://www.ip.co.za/people/kalle/project.htm#lcd
>
> Cheers     *<<<-|
> --
> Kalle Pihlajasaari   .....kalleKILLspamspam@spam@ip.co.za   http://www.ip.co.za/ip
> Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
> + 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

1996\12\17@235729 by Kalle Pihlajasaari

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Hi Tony,

> > >  I am having trouble initializing my 2x8 optrex lcd w/hd44780a

> indicated I should. Plus a few variations.Is it necessary to pull the
> unused inputs to the lcd low externally ?

Yes.

Cheers     *<<<-|
--
Kalle Pihlajasaari   kallespamKILLspamip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

1996\12\18@001827 by Chee Foon Tiang

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Kalle Pihlajasaari replied:

> Hi Tony,

>> I am having trouble initializing my 2x8 optrex
>> lcd w/hd44780a
>> Is it necessary to pull the unused inputs to the
>> lcd low externally ?

>Yes.

NO!!
The HD44780 is pulled-up internally, therefore, you
can just leave unused inputs open.

Regards,

Peter Tiang
.....tiangcfoonKILLspamspam.....hitachi.com.my

1996\12\18@033242 by Shel Michaels

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In a message dated 96-12-18 00:00:21 EST, Kalle anwered:

>> Is it necessary to pull the unused inputs to the lcd low externally ?
>
>  Yes.
>

Are you sure about that?  My interface _appears_ to be working fine, yet I
leave the four extra data lines DB<3:0> floating.  Am I likely to blow them
up or something?  The example code from Optrex, for 4-bit interface, doesn't
_use_ DB<3:0>

Best regards to all, and wishes for a happy season!!  8^)

Shel Michaels
Massachusetts, USA

1996\12\18@101442 by John Payson

picon face
> >> I am having trouble initializing my 2x8 optrex
> >> lcd w/hd44780a
> >> Is it necessary to pull the unused inputs to the
> >> lcd low externally ?
>
> >Yes.
>
> NO!!
> The HD44780 is pulled-up internally, therefore, you
> can just leave unused inputs open.

Generally true, but if you don't use R/W, you must strap it low.

1996\12\18@102121 by Kalle Pihlajasaari

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Hi Shel,

> >> Is it necessary to pull the unused inputs to the lcd low externally ?
> >
> >  Yes.
>
> Are you sure about that?  My interface _appears_ to be working fine, yet I
> leave the four extra data lines DB<3:0> floating.  Am I likely to blow them
> up or something?  The example code from Optrex, for 4-bit interface, doesn't
>  _use_ DB<3:0>

As Peter Tiang  mentioned they have pullups.  Having checked the data sheet
the only difference will be the mode that the display will be in
while you are setting it up for 4 bit mode, this intemediate mode
gets squashed by the 4 bit mode select command so it looks like it
won't matter which way you leave the low bits.  Letting them float will
consume a few microamps less perhaps.  Pulling them to ground will
prevent ESD from creeping into your display.

I ground them myself and it has always worked.

Cheers     *<<<-|
--
Kalle Pihlajasaari   EraseMEkallespam_OUTspamTakeThisOuTip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle

1996\12\18@112528 by David Schmidt

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Be sure you are waiting the required amount of time between instruction
writes to the display.

 I had trouble at first writing to displays in 4 bit mode and got
results like you see.  After I checked my code I found I wasn't quite
waiting long enough between writes.  Doubling the delays (for overkill)
worked!  I also found that the delays mentioned in spec sheets are only
approximate.  Increase yours and see if it helps.

Dave


At 02:08 PM 12/17/96 -0500, you wrote:
>Hello
> I am having trouble initializing my 2x8 optrex lcd w/hd44780a
>controller
>in 4 bit mode.I have tried everything I could glean from the FAQ's but
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1996\12\19@191401 by Tony Matthews

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I saw only millisecond delays in the spec sheet and in desperation
wrote delays loops several seconds long.nada
I suppose I must have damaged something?
       Thanks  Tony M.
David Schmidt wrote:
{Quote hidden}

1996\12\20@094244 by myke predko

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Tony,

>I saw only millisecond delays in the spec sheet and in desperation
>wrote delays loops several seconds long.nada
> I suppose I must have damaged something?
>        Thanks  Tony M.

Before you dispair, commit hari-kari, or go out and buy another LCD, there
are somethings that you can do:

1.  Check all your connections.  The first time I did an LCD Project (using
Walt Bank's code), I got nothing (and then noticed that the R/W line was
left floating...

2.  Make sure that what you are doing is pretty simple; ie just try to put
"A" on the LCD.  Don't go for the full implementation right from the start.

3.  Look for documentation; I didn't have a lot of luck with the FAQs on the
internet (a *lot* of problems/errors).  But, the Optrex Data Sheet from
Digi-Key (around $3.00) is pretty accurate (I've only found one
inconsistancy/error so far).  I've never been able to find a Hitatchi Data
Sheet for the 44780 (even from the local Toronto Hitatchi office) - they
seem to treat them like the family jewels.

4.  Even without anything valid, you should be able to turn up the contrast
and see the dots of the characters become visible.  If you don't see this,
look at your power and contrast connections.

5.  You can build a simple, manual controller using a dip switch (with
pull-ups) and a single-shot (ie 74121) and figure out what's the problem
pretty easily.

I've been there; I'm convinced that LCDs are pretty easy to use, just a real
bugger the first time.

Good Luck,

myke

Today, the commercial sector is advancing computer and communication
technology at a breakneck pace.  In 1992, optical fiber was being installed
within the continental U.S. at rates approaching the speed of sound (if
computed as total miles of fiber divided by the number of seconds in the year).

Aviation Week and Space Technology, October 28, 1996

1996\12\21@144334 by Tony Matthews

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myke predko wrote:
{Quote hidden}

year).
>
> Aviation Week and Space Technology, October 28, 1996
Your words of encouragement are appreciated and come at a good time.The
possible problems you suggested I tested long before.I suppose your
suggestion of manually operating the device is where I'll go from here
but unsoldering a ribbon cable is not much fun.Thanks Tony M.


'initializing a 2x8 lcd'
1997\03\04@132045 by Marianne Peters
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Please do not send any more mail to this address.  Thank you.

Marianne

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