Mystery LCD

What's the chip? There's a semi-standard interface for the HD44780 but it's 14 pins. I don't know what to tell you about the 15 pins. There are a number of webpages that talk about interfacing LCDs to PIC processors...and probably others. They'll have the details of the

If your luck is like mine, you've got bare chips on board covered with black goop and not a chip number in sight... mike

I don't see any chip that is directly associated with the LCD, and I can't find any chips mounted on the LCD itself ... the only chip is the one on the unit which is an Atmel ATmega128L. I don't want to destroy the LCD trying to pry the back off to find the controller chip...

Maybe it's a COG (chip mounted directly to the glass) LCD.

Best regards, Spehro Pefhany

Elliot, The standard interface (sort of standard anyway) is pwr,gnd,contrast,3 lines for control (E, RS, R/W), and 8 bits of data. I have a unit that has 16 pins but the extra pins are unused. I have the data sheets (PDFs) for both the HD44780 and a Samsung version (KS0072) that uses the same intruction set. Email me if you want either or both. Without the right intructions you can't get an HD44780 or compatible to do much of anything since you have to send the right command sequence to initalize them. Glenn Pavlovic

Your LCD may be made by Truly Semiconductors in China. One of their distributors in the USA, All American Direct, carries another LCD with a part number that starts with "CMF-TG" and lists Truly as the manufacturer.

Long Link to All American's listing of LCD with CMF part numbers:

Link to Truly USA:

Link to Truly in China:

-- Chuck Wozniak

snipped-for-privacy@eep.burdell.org wrote:

After some more investigation tonight, it looks like Truly is in fact the manufacturer; I was never able to get any more information off the LCD itself but I did peel back some tape on the ribbon cable and saw "Truly" printed on it with some another part number (TG400) that is similar to the one on the LCD.

It's definitely 16 pins (I mean it this time!) - two are ground, one is perhaps contrast of some sort (it appears to be connected to ground through a parallel resistor and capacitor). The remaining 13 pins are connected to the Atmel chip as follows:

... so if there are three bits for control (say to PortD), 8 bits for data (say PortC), that only leaves two remaining unknowns. It's a good start, I guess. Too bad I can't get at the program on the Atmel chip...

At first glance, the Truly web sites aren't all that helpful, but I'll try to dig in a bit deeper tomorrow.

Thanks

-- Elliott

Chances are that it's a standard HD44780-type interface if it is a small character type display module. As others have said, there are basically 14 pins, but sometimes two more in line that have to do with backlight optionally (and sometimes the backlight can be brought out there or to separate pins on some Truly displays). We used a whack of them about 7 or 8 years ago but had some problems with them.

Anyway, look for info on that interface and you'll find lots of data for that chip and compatibles. Also code examples that are probably full of bugs.

It sounds like they are using 8-bit data interface (many applications use 4-bit mode). It also sounds like they are powering the LCD from a port pin,if your tracing of the circuit is correct. Perhaps the contrast pin is being driven by a PWM output with a low-pass filter.

Best regards, Spehro Pefhany

Can you get the LCD to function in the current equipment? If so, does it appear to only display only text characters in fixed positions or can it display different sized characters and/or larger graphic elements?

If you can not get the display to function can you tell if the active pixel area consist of evenly spaced dots or if the dots are is small blocks (of maybe 5x8 dots) with gaps between the blocks? You can usually see the dot pattern while slowly rocking the display back and forth under a strong light.

Just trying to figure out if your display is a character module or a small mono graphic display. A character module may be fairly easy to figure out. A graphic module may be a bit tougher to figure out if uses a combination controller/driver IC.

When you say "ribbon cable" are you referring to a cable made up of some type of bonded round wire cables or flex printed circuit cable?

FYI, I work for an LCD marketing and distribution company but not related to to Truly in any way.

-- Chuck Wozniak

snipped-for-privacy@eep.burdell.org wrote:

Sorry, I thought I had mentioned this earlier but I guess I didn't. The display is a dot-matrix display and it can show text of various sizes, other character symbols (i.e. level bars), and graphics (logos and such). Amber backlit but monochrome.

By ribbon cable I mean one of those flat amber-colored (mylar?) strips with copper tracks (I guess this is the flex printed circuit cable). It plugs in to the PC board, then expands and has several surface mount devices (I didn't peel back the tape cover far enough, but I'm guessing they're resistors).

I sent an e-mail to Truly USA but based on past experiences with this sort of thing I'm not expecting much.

I would say that pretty much eliminates the discussion thread on the standard interface for a character module with an HD44780 controller.

I know someone who has a friend that works for All American. I'll pass a message along to see if that friend ever heard of your LCD.

-- Chuck Wozniak

snipped-for-privacy@eep.burdell.org wrote:

The response from Truly USA was:

"We are sorry that we cannot provide any support on this LCD since this is a Custom made OEM LCD."

So ... probably out of luck there. Eh.