Another HD44780 question

Using a 4-bit interface, I assume I should tie D0-D3 to ground. I have decided to enable the R/W line, and might be reading from the LCD. Should I put a resistor between D0-D3 and ground, or can they be directly connected?

Reply to
_
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On a sunny day (Wed, 06 Feb 2008 17:49:12 GMT) it happened _ wrote in :

It says leave D NOT connected.

Reply to
Jan Panteltje

My Optrex manual says to ground the lower nibble to use in 4 bit mode, but I have seen others that say to just N/C them.

Jim

Reply to
James Beck

All the ones I've used had the unused bits unconnected.

I suppose the Optrex manual is trying to save a little current, perhaps, that might be drawn if the inputs float up to mid-Vcc or thereabouts?

If you look at their initialization protocol it's clear that the actual values the parts sees on those pins are all "don't cares."

Reply to
Joel Koltner

On a sunny day (Wed, 6 Feb 2008 12:33:41 -0800) it happened "Joel Koltner" wrote in :

If I measure on those unused data lines I measure 4.98V. Possibly there is some internal pullup.

Reply to
Jan Panteltje

I'm not sure. Would it make a difference on a display that says the values are don't cares if they are grounded? I've never tried it.

Reply to
James Beck

values

If it got into "byte" mode, then you tried to read out a location with "ones" in it, the displays drivers would be running into a short circuit. So floating seems safest. Or pull-down resistors of course.

--

John Devereux
Reply to
John Devereux

that

values

I can see that as a possibility. I grabbed my Optrex "DOT MATRIX CHARACTER LCD MODULE USER'S MANUAL" (the caps are theirs) again, just to be sure, and it does say to 'ground' D0-D3 if using 4 bit mode. Maybe they have some series resistance on the lines? Maybe they hope the CMOS drivers hold up during a fault condition? Maybe it helps sell more displays. :)

Jim

Reply to
James Beck

that

values

Better to use pull-ups, if deemed necessary. Pull-downs would waste current & could put the inputs into indeterminate states. There are internal pullups (10-120uA on the HD44780U DB0?DB7, RS, R/W inputs) according to the datasheet, presumably the older chips and clones have them as well. Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

I've always left them unconnected in my tinkerings. IIRC, the HD44780 has internal pull-ups on the data lines.

Reply to
Anthony Fremont

that

values

OK, I just didn't think it would be good to have them wobbling around. Internal pull-ups so if not connected they are still predictable works for me.

Reply to
_

I leave them open.

Tom

Reply to
Tom2000

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