LCD Memory Writing

[Luckyborg]

I have found several good threads that helped me figure out how to write to the custom characters of an LCD, but I couldn't find anywhere including the data sheets on how often I can write to those memory locations. If I want to do an animation that updates every second, does that mean if I hit 100,000 writes after a day and a half I might start getting corrupted results? Hopefully someone has a better data sheet or has done some long term projects already.

Thanks
David
Matko
800-814-4053

[Melanie]

Your LCD probably doesn't use EEPROM for storing special characters but dynamic (or static) RAM. This does not have the kind of WRITE limitations that older EEPROM designs had. After all, your PC's RAM is updated thousands of times a second, if it had that kind of limitation your PC wouldn't last more than a minute!

How can you check whether you have EEPROM or dynamic RAM? Create a custom character, save it to LCD, power off, and check if it's still there a couple of hours later! If it's gone, then you're safe. If it's still there... well... you still might be OK...

Technology is in a state of continual flux, you have some new PICs on the market today that have many kB of static RAM (the kind that doesn't get erased when you power-off) and which doesn't have the EEPROM life-limit. There's also EEPROM's on the market that last millions of WRITE cycles - not just a 100k.

So, in summary, what I've written probably won't help you. Your LCD's Datasheet and/or manufacturers technical helpline is a better bet.

[Luckyborg]

Thanks for the help, I'll swap out my LCD with a new one for the day and test the original tomorrow. Thanks for the details explanation.

David

[rmteo]

....you have some new PICs on the market today that have many kB of static RAM (the kind that doesn't get erased when you power-off) and which doesn't have the EEPROM life-limit.

Which PICs have static RAM that doesn't get erased when you power-off?

[rmteo]

Too bad. I had high hopes for this.

[mackrackit]

From Micros web site

Static RAM or SRAM
Static Random Access Memory. Program memory you can Read/Write on the target board that does not need refreshing frequently.

Look to you data sheets. Many have SRAM.

[rmteo]

Does the static ram retain its contents when you power off?

[rmteo]

Anything?

[mackrackit]

Not on a PIC.

[Melanie]

Sorry, I haven't been paying attention to this thread... I implied (perhaps erroneously) that all Static RAM is non-voltatile (trouble when reading too many different manufacturers product Datasheets). Only some types are. I haven't gone through all of Microchips offerings so I can't answer if there is non-volatile RAM amongst their product range - a question that could be posed to their technical enquiry line.

[rmteo]

There are no Microchip (or Atmel, Freescale, Infineon, Renesas, ST, TI, etc.) offerings that have non-volatile Static RAM. The only MCU's with non-volatile RAM are a few from Fujitsu and Ramtron - however, their RAM is implemented as FRAM (ferro-magnetic RAM) which is quite a different technology altogether.

There are also external RAM devices based on the above mentioned FRAM and BBSRAM (battery backed Static RAM) from several sources.