What is the critical problem in LCD driver.

No, not at the interface to the glass/LCD level.

Because they don't.

On my understanding, there are some LCD chip provider.

What is their job?

Best regards, Boki.

Ian Stirl> > Hi All,

LCDs, at the most basic, physical level, are just cells of a special chemical (called liquid crystal - hence the LC in LCD). The special properties of the chemical is that if you apply a current through it it changes its transparency - mostly it turns "black" (it's more complex than that, it actually changes polarisation, this is a simplification). So, without any electronics the LCD screen cannot "talk" I2C. You need an LCD driver chip with I2C input to make the LCD understand I2C. So one answer to your question is that their job is to allow you to write to the LCD using the I2C protocol.

Of course, you can, if you want, connect wires directly to LCD cells to turn them on and off. But it quickly gets complicated. You see, you can't just turn a liquid crystal "on". If you do that you will damage it. To turn in "black" you need to turn in "on" and then "negative-on" repeatedly - basically you need to give it a full AC waveform from + to

- and back again. You can't simply go from + to 0, you need to go from

• to - or you'll damage the LCD. Obviously for a lot of cells this gets to be quite a chore to do yourself. That's why there are dedicated LCD drivers that does this for you.

How to communicate with the LCD driver depends on the model. The common Hitachi chip you find on most alphanumeric LCDs uses an 8/4bit parallel port. Some drivers accepts I2C or SPI input. Some expect an analog TV or VGA signal.

--- ON segments must be driven out of phase with the backplane, while OFF segments must be driven in phase with the backplane:

_ _ _ _ _ BACKPLANE _| |_| |_| |_| |_| _ _ _ _ _ SEGMENT OFF _| |_| |_| |_| |_| _ _ _ _ _ SEGMENT ON |_| |_| |_| |_| |_

-- John Fields Professional Circuit Designer

They're not "out of phase", they're merely inverted. To see this, change the duty cycle:

Cheers! Rich

Isn't the idea to eliminate the DC component? If not, what is the typical limit on an acceptable duty cycle to drive an LCD?

Yes, reduce the DC component to a negligible amount. 50mV is a typical spec. Given the low frequencies involved, that translates into a pretty loose timing spec.

But the above are only the simplest 'static' displays. Many, if not most, LCD displays these days are multiplexed.

See, for example, figure 14, for a triplexed display:

You still don't necessarily need dedicated display chips if you don't care much about component count and you need the lowest parts cost.

Best regards, Spehro Pefhany

Hi,

Thanks!

I think setup a I2C interface is not a problem.

How to driver these MOSs in a accurate/delicate voltage/status is a experiance/skill.

Best regards, Boki.

snipped-for-privacy@yahoo.com wrote:

Nice, that LCD drive system and at least one related chip garnered a few patents at the time.