Interface ucontroller to cell phone LCD?

Ryan

Hi,
Has anybody here successfully interfaced to a color cell phone LCD?· You can buy color displays for cell phones off of EBay for super low prices, and they'd make a great display if they aren't too hard to interface to.· Has anybody done anything like this?

Thanks,
Ryan

Paul Baker

I am presently working on such an interface, it is a SX based design. There is no possible way to directly interface such a LCD with a Stamp.

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Ryan

Awesome, let me know how it goes.

I'm planning to interface to either a SX or a TIMSP430 series.· I've tried googling, but can't find any specs/tips anywhere.

Paul Baker

Im curious why you are contemplating using a TI MSP430, is it that you are familiar with the device? The LCD functionality of the MSP430 wouldn't help since it is for a standard 7 segment LCD.

Either microcontroller requires a fast external RAM to hold the pixel data.

Designing an interface requires adherance to the LCD's waveforms specified in the LCD's pdf file.

The difficult part is that the refresh rate for such an LCD is in the MHz (my LCD's clock frequency is 3.56MHz), and as such you need to interleave the LCD signals with any other functions the microcontroller is performing, that and making sure the LCD clock signal is jitter free when switching between interleaved code sections. I have chosen not to call a single subroutine in the mainloop because the extra 3 cycles for the return from subroutine cannot be fit in (3 cycles to return, 3 cycles for next subroutine call + instructions to determine next subroutine call; and I have a maximum 7 cycles between LCD clock transistions to ensure a jitter free signal = no subroutine calls in the main loop).

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Ryan

I'm contemplating the TI MSP430 because of its larger RAM and Flash sizes. I would actually be using the TI MSP430F1xx series, which doesn't have the built-in LCD controller. The board has to do MUCH more than just the LCD, so I need alot of other resources from the microcontroller. I also really enjoy using the SX because of its incredibly high MIPS, but that 2K flash size constantly kills my project. And if the flash is big enough, I often run out of memory, since there is no actual built-in RAM. So I'll have to closely look at what I want to do to determine if a SX could be used.

I had no idea that the refresh rate was 3.56 MHz. If it's that high, I'm wondering if I'd be better off using an FPGA. That refresh rate would be quite tough to achieve with any microcontroller.

Again, thanks for the input! BTW, which phone's LCD are you using? Where didd you find a PDF spec for the LCD?

Thanks!

Paul Baker

To properly interface with a large enough RAM youll need more pins than the SX28 has, and the SX52 has 4k program space. You may need to have a seperate microcontroller as an interface to the LCD that takes commands from a different microcontroller. The refresh rate isnt 3.56MHz its 70 Hz, the 3.56MHz is the clock rate of sending data to the LCD so that all pixels are written to 70 times a second. And since a 3.56MHz clock cycle is both high and low (preferably 50% in each state), the toggling of the bit for the clock occurs at a rate of 7.12MHz. I dont think an FPGA would be any easier of a route.
Im using the SONY ACX705AKM, still in the prototype/preliminary code stage.

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