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PICList Thread
'PIC16C65A and LCD problem!!'
1998\11\06@150405 by Steven Kosmerchock

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Friends,
I am using an LCD (2X20) to display some results of a test performed by a PIC16C
65A. The PIC performs all of it's tests and display's the appropriate data for t
he appropriate tests. Unfortunately, the first two spaces on the top line seems
to have an incorrect character (It's supposed to be blank). The funny thing is t
hat when I unplug the LCD from it's socket (leave the PIC circuit powered up) an
d then plug it right back in, the "trash" characters aren't there anymore. But i
f I turn off the whole circuit and then restart it, the "trash" characters are s
till there. It's a mystery to me!? I would appreciate any/all help I can get!! T
hank you all!

                       Best regards,
                       Steven


Steven Kosmerchock
Email:  spam_OUTsteve.kosmerchockTakeThisOuTspamcelwave.com
http://www.geocities.com/researchtriangle/lab/6584

1998\11\07@142719 by Gavin Jackson

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part 0 1088 bytes
Just a thought.

-----Original Message-----
From:   Steven Kosmerchock [SMTP:.....Steve.KosmerchockKILLspamspam@spam@CELWAVE.COM]
Sent:   Saturday, 07, November, 1998 08:54 AM
To:     PICLISTspamKILLspamMITVMA.MIT.EDU
Subject:        PIC16C65A and LCD problem!!

Friends,
I am using an LCD (2X20) to display some results of a test performed by a PIC16C65A. The PIC performs all of it's tests and display's the appropriate data for the appropriate tests. Unfortunately, the first two spaces on the top line seems to have an incorrect character (It's supposed to be blank). The funny thing is that when I unplug the LCD from it's socket (leave the PIC circuit powered up) and then plug it right back in, the "trash" characters aren't there anymore. But if I turn off the whole circuit and then restart it, the "trash" characters are still there. It's a mystery to me!? I would appreciate any/all help I can get!! Thank you all!

                       Best regards,
                       Steven


Steven Kosmerchock
Email:  .....steve.kosmerchockKILLspamspam.....celwave.com
http://www.geocities.com/researchtriangle/lab/6584


1998\11\07@142758 by Peter L. Peres

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On Fri, 6 Nov 1998, Steven Kosmerchock wrote:

> Friends, I am using an LCD (2X20) to display some results of a test
> performed by a PIC16C65A. The PIC performs all of it's tests and
> display's the appropriate data for the appropriate tests. Unfortunately,
> the first two spaces on the top line seems to have an incorrect
> character (It's supposed to be blank). The funny thing is that when I
> unplug the LCD from it's socket (leave the PIC circuit powered up) and
> then plug it right back in, the "trash" characters aren't there anymore.

The LCD needs to be initialized according to the data sheet sequence, or
reset by a fast power on flank. When you remove it from the socket and put
it back you do just that. The power on flank for the whole circuit is much
slower.

If you don't want to use the whole funky initialization sequence, use a
transistor switch to turn on the LCD power abruptly from a PIC pin or
from the reset chip that drives the PIC (if any).

> But if I turn off the whole circuit and then restart it, the "trash"
> characters are still there. It's a mystery to me!? I would appreciate
> any/all help I can get!! Thank you all!

The HD47xxx chips are genuine CMOS parts and as such they will keep the
bit patterns for several seconds or minutes without power applied (using
the very low voltage remaining in the decoupling caps). It is known that
some CMOS timekeeping chips need to be shorted without power applied for
up to 5 minutes to convince them to forget some of what they contain.

If you use the initialization sequence with the LCD it will be erased
properly by the time it lights up.

imho the missong reset pin from the industry standard LCDs is a pain in
the rear.

Peter

1998\11\07@142811 by Brian Striggow

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You could throw a rock in any direction and hit someone that knows more
on this topic than I do.  But in my limited experience, if 'junk' appears
on the pins of an LCD display, just about anything can happen, most of it
defying logic.  Try checking

Power up sequencing

Double check what you're actually sending the display

Check for adequate timing between rise and fall on enable line.

On Fri, 6 Nov 1998, Steven Kosmerchock wrote:

> Friends, > I am using an LCD (2X20) to display some results of a test
performed by a PIC16C65A. The PIC performs all of it's tests and display's
the appropriate data for the appropriate tests. Unfortunately, the first two
spaces on the top line seems to have an incorrect character (It's supposed to
be blank). The funny thing is that when I unplug the LCD from it's socket
(leave the PIC circuit powered up) and then plug it right back in, the
"trash" characters aren't there anymore. But if I turn off the whole circuit
and then restart it, the "trash" characters are still there. It's a mystery
to me!? I would appreciate any/all help I can get!! Thank you all! > > Best
regards, > Steven > > > Steven Kosmerchock > Email:
EraseMEsteve.kosmerchockspam_OUTspamTakeThisOuTcelwave.com > http://www.geocities.com/researchtriangle/lab/6584
>

1998\11\07@142950 by silicontao_roy

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I had the same problem with an LCD that I am doing. I made a refresh
function to fix it. The data does not change but the refresh function
re-draws the display anyway. I don't know what your problem is but my
problem is in the LCD it self. Yours may be or not but try refreshing it if
you are not already.

{Original Message removed}

1998\11\07@145139 by Mark

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> Friends,
> I am using an LCD (2X20) to display some results of a test performed by a PIC1
6C65A. The PIC performs all of it's tests and display's the appropriate data for
the appropriate tests. Unfortunately, the first two spaces on the top line seem
s to have an incorrect character (It's supposed to be
blank). The funny thing is that when I unplug the LCD from it's socket (leave th
e PIC circuit powered up) and then plug it right back in, the "trash" characters
aren't there anymore. But if I turn off the whole circuit and then restart it,
the "trash" characters are still there. It's a mystery to
me!? I would appreciate any/all help I can get!! Thank you all!
>

Sounds like they might be part of some sort of auto baud-detect.
The first few baud rates failed (and the check character shows as
garbage) and the last one was right. Once the baud rate is
established, you could disconnect and re-connect the LCD without
re-handshaking.

You didn't say much about the LCD so I'm just thinking aloud
here...


Mark Hillier
President, HVW Technologies
Markspamspam_OUTHVWTech.com
Tel:(403)730-8603 Fax:(403)730-8903
Visit our web site: http://www.hvwtech.com

1998\11\07@194126 by evan

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I had the same problem initially, even after meeting the power-up spec, on a
HD47xxx display.  Using the fancy software intialization sequence cleared
everything right up.  Besides, every decent software design should always
reset all peripherals after power-up (learned that the hard way).

-Ed VanderPloeg
Agile Controls
@spam@evanKILLspamspamdirect.ca

> {Original Message removed}

1998\11\07@225803 by Michael Hagberg

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yes, it's probably the init routine. here is a quick note from my data
specs,

power on

wait more than 15ms after vdd rises to 4.5vdc

write 0x30 function set

wait more than 4.1ms

write 0x30 function set

wait for more than 100us

(then resume normal data transfer)

michael

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{Original Message removed}

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