Connecting the LTD222QV-F01 2.3" QVGA LCD (LCD-08843)

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Postby Dan_attacker » Mon Sep 15, 2008 6:34 pm

mikeselectricstuff wrote:I came to the conclusion that a CPLD plus 16 bit wide parallel SRAM chip is probably going to be the lowest cost general-purpose solution, as low-end CPLDs and SRAM chips are cheap.


I did this for my last lcd project that used a ACX705AKM lcd with a 65535 x 16 SRAM. I used a 9572 CPLD and I was at around 80% capacity with my code and I only had 9 data lines. The QVGA lcd having 18 data lines and requiring more address lines for the larger SRAM would probably put the logic over the capacity of a 9572. I could be wrong however, because I'm still very new to vhdl and write sloppy, inefficient code. Anyways, I decided to just go with a cheap FPGA and put in an SPI interface for simplicity for connecting to the MCU.

Edit: Actually, it might have been around 60% capacity. I can't remember.
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Postby mikeselectricstuff » Tue Sep 16, 2008 1:05 am

Yes - the datapath could be a resource hog - I've not yet looked at it in enough detail but was considering maybe pulling that out of the CPLD with some bus switches etc. or maybe using an 8 bit RAM, 8 bit path to the CPU and an external 8 bit latch to fan it out to 16 bits just before it hits the LCD.
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Postby Dibblah » Tue Sep 16, 2008 11:37 am

On a slightly separate topic, but still small LCD related, I came across this page:

http://semcblog.com/other/displays/

Which lists the display controller used in a large number of Sony Ericsson mobile phones. Cross referencing this with datasheets (which some of these controllers actually have!) and ebay shows that you can get a 320x240 display with integrated RAM controller for under £20, after shopping around.

Not nearly as cheap as $1, but far easier to interface with!

Cheers,

Allan.
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Postby mikeselectricstuff » Tue Sep 16, 2008 11:51 am

Another option for a cheap QVGA with RAM might be the ipod display, which can be got as a Hong Kong clone for about £10.
Only problem is sourcing the nonstandard 32 way 0.3mm pitch FFC connector - I enquired with the maker and min order qty is 7500 (@ GB£0.70 each). It may be possible to use the more obtainable 33 way one with care.
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Postby doctek » Wed Sep 17, 2008 7:35 pm

The good folks at Renesas SP Driver have come through with an actual hd66790 Data Sheet! In response to my begging letter, they responded.

What is the best way to make this available? I'm open to suggestions. I'm going to offer to email it to SparkFun directly, but what else could I do?
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Postby Narkaleptic » Wed Sep 17, 2008 8:04 pm

I am successful!!!

HD66790R Datasheet [3mb]

As we suspected:
To our regret, this product is production stoped.
There is no product similar to the function that this product is achieved now.
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Postby Johey » Thu Sep 18, 2008 12:59 am

Narkaleptic wrote:I am successful!!!


Brilliant! Now there's hope... :) I've ordered another batch.
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Postby mikeselectricstuff » Thu Sep 18, 2008 1:47 am

Like buses they all come at once.... I got the DS yesterday afternoon from a friend who had a contact at Renesas - was waiting to check if it was OK to distribute but looks like it's escaped now - maybe Renesas got tired of all the requests..! Someone also emailed me another version this morning.

One detail - the one I have is for the HD66790, the one posted above is the 66790R. I've had a a quick scan through & apart from quite a few differences in phrasing (maybe different translations from Japanese), the only technical difference I can see is that the 66790 does not have the IFS bit in R06. Some quick tests indicate that this bit is not present in these modules, so we are dealing with the 66790 not he 667790R.
Here's the HD66790(no R) version

Incidentally, both of these datasheets have a typo - the address for the "Power Color 1" register should be 00 not 01. This is confirmed in the register summary table .
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Postby JamesK » Thu Sep 18, 2008 4:28 am

Fantastic news on the datasheets, many, many thanks.

Now it really is time for me to try and get one connected up. Plan A is to try and solder wires directly to the tab, but clearly I'm going to need to make a pcb in the longer term. I've always worked with strip board before, can anyone offer some tips for getting started with pcbs? How practical/expensive is home manufacture? Or should I just go with the pcb service from Sparkfun?

Regards,
James.
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Postby mikeselectricstuff » Thu Sep 18, 2008 5:01 am

JamesK - see my PCB page for info on homebrewing PCBs.
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Postby mikeselectricstuff » Thu Sep 18, 2008 5:25 am

I've now updated the initialisation sequence on my page in the light of the datasheet. This appears to be reliable and produces a reasonable greyscale.
There will be some scope to tweak the gamma adjustment registers for best appearance, but this will have to wait to we can get some decent test images to look at.
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Postby Dan_attacker » Thu Sep 18, 2008 5:35 am

Nice work to both of you guys for getting the datasheet!

I'd like to get started with these LCDs as well as finishing up with the PSP LCD, but my LPC2148 stopped working probably due to a poorly homemade PCB. I'm in the process of redoing how I build PCBs so it will be a while until I'm up and running again. But I'll post some pics when I get my LCDs working.
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Postby JamesK » Wed Sep 24, 2008 5:18 am

Here's my best result so far:

Image

Soldering loose wires to the connector is possible, but really painful - not recommended.

Sadly things aren't as rosy as they look. I'm driving from a PIC, so 5MHz dotclock is out of reach. The above was running at about 248 kHz. It looked pretty good, but that's the view from the back. When I flipped it over to mount it properly on the backlight it looks much worse, with a really nasty scrolling white/yellow bar. There's a long way to go before I have something usable!

James.[/img]
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Postby silic0re » Wed Sep 24, 2008 8:48 am

Still, that's looking quite good compared to where everyone was a week ago! :)

If you happen to have access to a dsPIC, I drove a Sony ACX705AKM 320x200x9-bit display directly from a dsPIC30F3012 without too many problems -- they can get up to 40MIPS, so if you optomize your code you can display various patterns on the screen at up to a few FPS, If I remember correctly. Of course that's only a short-term solution :)

best of luck!
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Postby mikeselectricstuff » Wed Sep 24, 2008 5:00 pm

JamesK wrote:Here's my best result so far:

Image

Soldering loose wires to the connector is possible, but really painful - not recommended.

Sadly things aren't as rosy as they look. I'm driving from a PIC, so 5MHz dotclock is out of reach. The above was running at about 248 kHz. It looked pretty good, but that's the view from the back. When I flipped it over to mount it properly on the backlight it looks much worse, with a really nasty scrolling white/yellow bar. There's a long way to go before I have something usable!

James.[/img]

Remember that you don't necessarily need to deliver a new pixel on each pixclk - you can still get reasonable res using every 3rd,4th etc. pixel.
An SPI peripheral can make a good output shifter, and PWM/compare peripherals can be used to generate pixclk & hsync, and with some fiddling you can usually get them to stay in sync.
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