Hi,
Most of the things I design don't have traditional displays, so... :<
Aside from mechanical differences in connectors (a consequence of the number of "color bits"), can I safely design a generic LCD interface without preselecting the actual display panel?
I'm looking at small-ish panels (3" - 8") with an emphasis on low power consumption.
Is there a magic cutoff point between LED backlighting vs. CCFL's? (i.e., this would impact the controller's design as well)
Thanks!
--don
You can have Intel or Mot styles, 1 or 4 bits serial, 8, 16 or 32 bits parallel. With / without backlite. With / without touch panels. So, the short answer is probably not.
CCFL needs 40V to 50V minimum. So, LED is easier for most people to handle.
Are you building the controller yourself? A QVGA panel requires 500+ signal lines.
Huh? I'm talking about the bare *panel*, not controller.
Touch panel is a separate issue and addressed via touch panel interface (from what I have seen, the touch panel is a seperate assembly, seperate connector, etc. -- even if it is purchased "married" to the display panel)
Most of the CCFL inverters I have seen were ~12V powered.
Regardless, my question was trying to determine if there is a *size* beyond which LED is impractical (inefficient in terms of cost).
s
there's a step between bare panel and full controller with build in framebuffer etc.
signals are something like; vsync,hsync, R,G,B(~6bits each) and a clock. either as seperate lines or serialized onto a few LVDS lines
-Lasse
ts
+Yes, this is one way of interfacing to an unbuffered controller.
Other ways are 1 or 4 bits serial, 8, 16 and 32 bits parallel, Intel or Motorola signalings, etc.
There are dozens of standards.
Exactly!
I want to know how "standardized" the signals presented via the "flex circuit" tail are. Aside from differing numbers of "color bits", do all panels use the same basic signal sets? I.e., how reasonable is it to expect a controller to talk to a wide variety of panels (assuming the connections can be mechanically accommodated) without requiring significant hardware (electronics) changes.
E.g., controlling CCFLs is different than an LED backlight.
(4/5 wire resistive touch is different than SAW, etc.)
Thanks for clarifying that!
--don
ts
+as far as I can tell they are all more or less the same, only difference is is timing and that should be programmable in the controller
the parallel to seriel are standard chips such as:
-Lasse
The Thine Controller seems to be more popular, 18bit and 24bit LVDS.
Cheers
You cannot. Selecting an affordable panel is a world of pain. Make sure you can get the cables as well!
-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
More or less. If you have hsync, vsync, pixelclock and RGB data you'll be fine to drive CMOS interface style displays (up to about
40MHz pixel clock). Expect displays to have different timing requirements though. Some displays have a data-enable signal but this is usually more trouble to create than its worth.-- Failure does not prove something is impossible, failure simply indicates you are not using the right tools... nico@nctdevpuntnl (punt=.) --------------------------------------------------------------
Hi Don, more or less they do, lately I am witnessing them to also specify a *minimum* clock frequency. On older TFT displays one could lower the clock frequency at will until the colours began to degrade (because of TFT gate leakage), now this seems to have changed, perhaps they have some PLLs or sort of. But I am not sure, have not fought any such wars, just an observation while considering various parts.
Fairly reasonable, if you get a controller, that is. The last monolithic one on the market was the b69030 by Chips/Intel/Asiliant, now there are some hybrids by a Taiwanese manufacturer (this applies if you are looking for VGA and above resolutions). Some SOC parts do come with a display controller as well (unfortunately none I like is still really on the market, the closest was the MPC5121 but one of its errata said "the SATA interface won't work; workaround: don't use SATA....). I am eyeing one of their new QORIQ parts now but it seems to be still far from anything really usable, let's see if they will make it (I do hope they will).
Usually backlight is not considered part of the "controller" interface, the controller has some TTL output to drive it on/off, I usually use some GPIOs to make up some sort of DAC to drive the intensity and that's it. If you want to be able to use both LED and CCFL backlit panels you will have to design in both power sources somehow (not a huge issue since CCFL usually need a tiny convertor board anyway, one could simply change it as needed).
Dimiter
------------------------------------------------------ Dimiter Popoff Transgalactic Instruments
------------------------------------------------------
I'm in the middle of trying to find sources for a small QVGA panel, there seem to be some "almost compatible" COG chips (from Taiwan). The chips are a bit strange since they don't need to be packaged, they are shaped like matchsticks. Anyway, several seem to use a common FPC pinout but even then all the modes may not be available (and the most tempting modes to omit probably the ones *you* would want- the ones that are not used for video display).
Best regards, Spehro Pefhany
-- "it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
They are designed to be mounted directly on the glass, usually 0.1mm pitch.
LCD does not need hsync and vsync. There is no beam to retrace anyway.
Hence I use the term "COG" = Chip On Glass.
They have sync signal inputs, presumably to reset internal counters. "Video" input is RGB digital parallel. Gamma and so on is dealt with by an auxilliary SPI interface.
Or, perhaps an onboard buffering just preserving a "classic interface"?
I'm just trying to reduce the number of variables in the design process. I.e., if I can pick a controller and design around that and *later* pick a display panel, that's much easier than waiting until *all* of the choices have been made and then rushing to accommodate all of them in a cohesive design.
Yes. In my case, I want to put all of the display interface on a small board (LCD interface, backlight, touchpanel, etc.). So, if I end up with a panel that has LED backlighting, I need to have provisions for that on my board. Likewise, if I aimed for a CCFL backlight, then I would need the hooks to turn that backlight on, vary it's intensity, detect faults in the inverter, etc.
I'm just trying to gauge what approach is safest to follow.
--don
...........
yes, your approach is good. Stay away from COG if you are looking at minimal changes from supplier to supplier, since everyone seems to pick a different COG controller.
The 16 or 24 bit interface is fairly standard (although the connectors vary from supplier to supplier.) Many of these also include a I2C channel to manage setup information.
Here's a development kit from Renesas that uses a "standard" TFT LCD interface to talk to many different panels using an intermediate connector board based on the LCD supplier.
--Vinnie
What do you suggest other than COG?
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.