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PostPosted: Thu Jan 20, 2005 3:51 
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coorz wrote:
I remember having read somewhere that LCD's on a laptop's LPT might not work always. Have you tried the LCd on a normal PC?


Yes, i've tryed on 3 different PC's, one laptop and 2 desktop's.

Henri, were to did you send the exe?

Syridian: i've made the following connections...

All GND's go to GND of USB and GND of LPT (as show in pic schematic Henri give for this controller) All +5V go to USB +5v. the rest is direct cables from lcd to lpt. i've checked for shorts and none reveal, all connections look fine and a continuity test is ok for all cables. I'm using IDE falt cables (all splitted).

thank you all :)

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PostPosted: Thu Jan 20, 2005 3:53 
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I forgot to mention... the lcd only stays on (even without the USB power on) in the Desktop's computers, in the laptop it goes off immediatly.

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PostPosted: Thu Jan 20, 2005 3:56 
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I take it you checked the voltage with the Backlight connected and disconnected? :) (I'de love to track down where that current for the backlight is comming from, but as Henri said... He's seen it before.. so I don't think that wuld be causing your problem.

Hmm... well, I'm stumped... over to the software guru I think. ;) Try out his software when it turns up... he probably emailed it... maybe... Let us know how you go. :)

Edit... The LCD stay's on? Or the backlight? That could explain the current through the LPT port... I have tried powering an LCD from the LPT port on my laptop, and it struggles to even get enough power to work without any backlight... but I haven't tried it on a desktop yet... Might have decent IO drivers in a desktop machine providing the needed current. Still, check the voltage when the backlight is connected and powered through USB... I may be wrong... But I would still be interested to know if it's still +5volts.

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Last edited by Syridian on Thu Jan 20, 2005 6:02, edited 1 time in total.

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PostPosted: Thu Jan 20, 2005 4:26 
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Syridian wrote:
I take it you checked the voltage with the Backlight connected and disconnected? :) (I'de love to track down where that current for the backlight is comming from, but as Henri said... He's seen it before.. so I don't think that wuld be causing your problem.


i havent checked voltages yet... not enough time unfortunnaly :(

Syridian wrote:
Hmm... well, I'm stumped... over to the software guru I think. ;) Try out his software when it turns up... he probably emailed it... maybe... Let us know how you go. :)

Edit... The LCD stay's on? Or the backlight? That could explain the current through the LPT port... I have tried powering an LCD from the LPT port on my laptop, and it struggles to even get enough power to work with any backlight... but I haven't tried it on a desktop yet... Might have decent IO drivers in a desktop machine providing the needed current. Still, check the voltage when the backlight is connected and powered through USB... I may be wrong... But I would still be interested to know if it's still +5volts.


The backlight is on without power on the desktops, but in laptop it's off. There is no pixel on the screen in both situations. I'm going to wait for the exe file from Henri and see what it does...

:)

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PostPosted: Fri Jan 21, 2005 3:37 
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Let me know about that voltage when you can measure it...

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PostPosted: Fri Jan 21, 2005 9:20 
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ignatz wrote:
Henri, were to did you send the exe?

I just replied to your last email, let's see, it was gmail.

If you don't receive anything let me know.

EDIT: I just noticed your PM. I'll send it again when I get home.


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PostPosted: Sat Jan 22, 2005 3:18 
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ok...first thing...the voltage measured without the USB pluged in (the USB only gives +5v, no data thru it)

Pin1 VSS Pin2 VDD - 3.68v

Pin19 Anode Pin20 Kathode - 3.62v

With the USB pluged IN (powering backlight and 5v rails for LCD)

Pin1 VSS Pin2 VDD - 5.06v

Pin19 Anode Pin20 Kathode - 4.89v

i already got the EXE file for testing sended by Henri (thank you once again:) )

I've run it (i'm under windows 2000) on a command prompt dos window and nothing happend...

Henri, any suggestions?

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PostPosted: Sat Jan 22, 2005 12:58 
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That voltage in the VDD pin looks ok with the power plugged in.

Have you tried different parallel port settings in BIOS ? These can often affect how well the parallel port works with lcds. I have usually used ECP/EPP mode but it's probably worth testing them all.

Also still double check your wiring that everything goes as in the schematic I made. When I wired my display I accidentally wired the C86 pin wrong and spent few minutes wondering why the screen stayed blank.

If nothing still happens after these steps I'll do some modifications to the timings.


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PostPosted: Sun Jan 23, 2005 3:03 
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hi!

i've checked and double checked (even with a multimeter) the connections and they all go like the wiring you gave me with the driver

Image

the datasheet of the LCD says that the C86 input must be HIGH (+5v) if using 6800 series microprocessor or LOW (GND) if using the 8080 series microprocessor. Wich one is the right one? i'm asking this because you told me you had problems with this input.

Anyway, i've tryed to change the settings for the LPT but my laptop only gives me the chance to change the address from 378 to 278... there is no ECP/EPP or other modes available (wich i see as a fault of the bios, they are ussually available in all bios settings). I'm going to keep on working on this tonight (the night shift is always good for this hehehehe ), and later on i'm going to try it at home with a computer that has the other options for the ECP/EPP modes ;)

i'll keep you noticed if there are any changes, but to be honnest, i'm not to hopefull ;)

:)

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PostPosted: Wed Jan 26, 2005 2:14 
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Well... i'm back

After 2 days off work @ home, i've tested the LCD on 2 different computers, both with WinXP SP1. I've tested all settings for the LPT in BIOS, but none of them worked. The LCD just stays with the backlight on and nothing shows. :(

henri... any suggestions?

thank you :)

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PostPosted: Wed Jan 26, 2005 3:55 
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OK.... Time for me to have a serious look at this instead of just throwing idea's at you.

Do you have the actual datasheet for your display? Could you either post me a URL for a location of it online or mail it to me? :) To me it still seems like it might be a wiring problem of some sort, it's too catostrophic a failure for it to be just a driver issue, considering that Henri would have tested it on his display and had it working before release. You should be able to get something.

Actually... Ummm... Being obvious here... and not remembering the full conversation previous... Have you fiddled with the contrast pot with the display powered? Power up the display, wind the contrast pot fully one way, and then fully the other. What you are looking for is for the display to turn black. When you find that point that it does, wind it back a touch so that the display isn't black anymore. Or, if you have data being displayed on the screen, find the best contrast for your needs.

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PostPosted: Wed Jan 26, 2005 5:05 
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Ok...now you got me... contrast POT??? damn... dont tell me it's that... i'm not using a contrast pot in the LCD, as i just follow the wiring Henri posted with the driver... i'm going to mail you the Datasheet for that LCD.

:)

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PostPosted: Wed Jan 26, 2005 6:31 
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Hmmm.... ok.. the LCD doesn't actually use a contrast pot... sorry... I should have realised that from the wiring schematic. The contrast is set digitally.

Do you know if there is a configuration option in the driver that Henri sent you to adjust the contrast or LCD bias? Hmmm... need to get back on my computer and test that myself...

I'll get back to you after I have played with the driver later this afternoon... hopefully.

BTW... Nice module, just been looking over the datasheet you sent me. Some nice options in there. I'll have to familiarise myself with how many of those options the driver takes advantage of.

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PostPosted: Wed Jan 26, 2005 9:33 
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Here's still a link to the datasheet:
http://www.topwaydisplay.com/Product/pd ... Rev0.1.pdf

Contrast is something that could explain why nothing shows. There is no contrast setting in this version of the driver yet. But I think even if the contrast setting would require adjustment there should be shown something even now that the default value recommended in the module datasheet is used.

C86 should be wired high like in the schematic. The schematic should be the exact way how I connected the display as I first made the schematic and then connected my display based on that.
I noticed that the display stays just blank even if you connect power and something happens only after the initialisation is executed and the commands to enable the display are sent to it.
This was clear when I had the C86 connected wrong and because of that the display didn't understand the commands I tried sending it and didn't show any signs of life.

Like Syridian said it seems strange that nothing shown on the lcd. Even if there was a timing problem I would have expected garbage but maybe if the timing problem is severe enough it can't succesfully write the configuration to the display to enable it.

I could also add option for the LCD bias setting. There are two options and in my testing the other option just made the display completely black.

I'll do some changes to the driver today and also check the wiring again.


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PostPosted: Wed Jan 26, 2005 19:22 
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Just as an FYI ( I don't think anyone corrected this ) the maximum current *as per spec* on a single USB channel is 500mA, far in excess of what is needed for the backlight + logic. However most controllers support upwards of 1A per channel. It is also per spec to have overcurrent protection, so the port will power off if the current goes too high. Thus is is pretty much guaranteed to be +5.0V all the time.

It is not uncommon with ICs for there to be leakage from data/control pins if Vcc is not present. I.e. if you remove power, however some of the data lines from the parallel port are high (with respect to the ground from the parallel port) then the logic can remain powered. The current required for logic of the LCD controller is in the range of 50-100uA (microamps or 0.05mA). Standard LED backlights require somewhere in the range of 100-300mA, so it is unlikely that the LEDs can be powered from the // port if the power has been removed. It is possible, however, to remove power, wait a while, and then plug power back in and the LCD will still be displaying the same thing because the LCD controller chip drew all necessary power to remain in standby from the // port pins. For this reason I recommend to lower all signals from the // port to the LCD prior to closing the application / whatever.


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