Code that worked with WINDSTAR LCD doesn't work with Newhaven LCD?

[jellis00]

On many chips, RA4 is Open-Collector and won't drive the pin high on it's own.

I'm assuming you're still using an 18F4550.

The datasheet doesn't specify, but in ISIS with an 18F4550, the LCD won't initialize without a pull-up.

It could just be a simulator thing.

Try it.
Stick a pull-up in there.
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Tried a 10K pull-iup on RA4 and still no characters appearing on LCD. Going to hook up oscilloscope next to the various LCD interfaces to see if I can figure out what is going on.

I don't know what ISIS is or what you mean by it could be just a simulator thing. Is ISIS a simulator?

For your info I asked Microchip tech support about whether RA4 on 18F2550/4550 is open-collector or not and whether there should be any problem of it driving RA4 high with an LCD interface and here is their response:
----
Hi,
Thank you for contacting Microchip Technical Support.
RA4 can drive the pin High, please configure all the Port pin of PortA to digital by setting the bit in PCFG0-PCFG3 in ADCON1 Register.
For further assistance, do write to us with the following details.
1) Please attach your code along with MPLAB IDE workspace.(MCP and MCW files)
2) C18 -Version?
3) MPLAB version?
4) Screen shot of the disassembly listing in the view tab.
Awaiting for your reply
Thanks & Regards,
Microchip Technical Support

[falingtrea]

Also could be as simple as a contrast voltage issue (Vo). Do you have a pot on the Vo pin?

Also noticed pin 15 and 16 of the New Haven display are listed as NC in the data sheet, but the example schematic shows them as A+ and K- and shows then both grounded. So maybe you need some clarification from New Haven on how to connect up the display.

[jellis00]

Also could be as simple as a contrast voltage issue (Vo). Do you have a pot on the Vo pin?

Also noticed pin 15 and 16 of the New Haven display are listed as NC in the data sheet, but the example schematic shows them as A+ and K- and shows then both grounded. So maybe you need some clarification from New Haven on how to connect up the display.

Yes, I have a 20K ohm potentiometer connected as a Vo source for controlling contrast. I see the black matrix dots on the 1st line of the display when I power up with the pot set near 0 ohms....that is how Newhaven said I could tell if the LCD is alive and well and hasn't been zapped.

You are right, that on the prototype PCB pins 15 and 16 are connected to ground...did that because that is wn on scheamtic on Page 4 of the LCD data sheet.....but we checked with Newhaven tech support and they said it doesn't make any difference whether pins 15 and 16 are grounded or left un connected for this particular module that doesn't have a backlight.

Thanks for the comments, anyway...they help me keep thinking.

[mark_s]

Did you see the data sheet for line addresses? Look for "DDRAM" bottom page 6 in the LCD data sheet.

Also have you set ADCON1 to %00001111 for all digital on porta?

[Byte_Butcher]

Are you SURE you have the pinout correct on the New Haven display? It MAY not be the same as the windstar...

I know nothing of Windstar, but I use quite a few Lumex displays, and have recently started using some New Haven displays, and the pinout on the NewHaven that I'm using is NOT the same as the Lumex.

Lumex :

Pin1 = Ground
Pin2 = Vdd
Pin3 = Contrast adjust

New Haven:

Pin1 = Ground
Pin2 = Contrast adjust
Pin3 = Vdd

All other pins are the same except for 2 & 3 being swapped between NewHaven and Lumex.
Can't vouch for the Windstar, but you might want to have a look at the data sheets again?


Steve

[Darrel Taylor]

... and the pinout on the NewHaven that I'm using is NOT the same ...

Awesome!
Didn't see that coming, and I was looking at the datasheet, which agrees with you.

Easy enough to test.
Jellis, If you turn the contrast pot the other way, does it start smoking?
OK, probably not the best way to test it.

Add: Probably wouldn't anyway's, rats.
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[malc-c]

I had a similar issue with a 16 x 2 LCD, which turned out required a voltage range between -5v and +5, and seemed to offer the ideal contrast when the voltage was around -3.5v

Not saying this is the cause (haven't looked at the datasheet for your display), but it did catch me out.

[Byte_Butcher]

When I bought my Newhaven displays, the pinout difference stood out immediately to me in the data sheet.
On the Lumex, and all other displays I've used, the Vss, Contrast, and Vdd pins are laid out in a row with the contrast in the middle like the pins on a pot usually are, with a voltage across the "outer" legs and the wiper in the middle.

The out of sequence power / contrast / ground sequence caught my eye right off.

Sorry I didn't mention it sooner. I didn't think about it until the word "Newhaven" came up again in one of the later posts and sparked a brain cell....

I hope that's the problem for Jellis00 !


Steve