CF635 "power-on" display

[omegaman]

I need the CF635 to display a "power-on" message the instant (+5VSB/USB/battery) is applied. However, the "power-on" display only appears/lights up when the USB *driver* initializes the display.

The specifications state:

The CFA-635 loads its power-up configuration from non-volatile memory when power is applied. The CFA-635 is configured at the factory to display a “welcome” screen when power is applied.

Is this incorrect??? Any way to "power-on" when power is applied?

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[omegaman]

Well I found the following in another message :

The bootscreen editor is a little useless with the USB LCDs, since they dont "light up" until windows has loaded.

The serial LCDs will show the boot screen from when the PC is turned on, until windows/software loads.

Who's bright, or should I say *dim* idea was that?

Begs the questions:

Why is USB different from serial in this situation?

What does the interaction with the windows driver do to initialize the display to"power-on" state?

Why isn't this initialization on power-*up* a display command option??????

 

[jdgordon]

dont take my word for it.. but i think u get to blame the OS for this...
if the os doesnt turn the usb ports on untill its ready to (as in almost ifnshed loading in the case of XP) then u wont c the welcome screen.

so u got 2 choices to get around this... either buy a scab and plug the floopy power connector into that (then the lcd will turn on when the comp turns on..
OR you could hack up the usb connector to get the power from the psu instead of usb (make sure u use the RED wire, NOT YELLOW), you might want to stick a resistor in there also to not fry the lcd... maybe... i dunno..

i know for sure getting a scab and useing its power works (iv got this setup)
________
Vaporizer instructions

 

[omegaman]

Hmmm....I was under the impression that USB +5v was sourced by the system board at power-up. You're saying the USB port power is switched by the OS when the drivers load?

Lack of power would certainly explain the problem! I will put a meter to it tomorrow and see. Also easy enough to rig +5v from an ATX PSU to test the CF635.

I can rig a WOL cable to provide +5VSB, just like the SCAB if all looks good.

Thanks for the tip.

 

[omegaman]

I applied +5v to the display from an ATX PS. It's getting +5v but it does NOT initialize and light up! This is not what the CF635 specs say.

 

[CF Tech]

If you want it to power up right away, you need to power the module through H1 (see page 8), and open JP2 (see page 27).

ref: http://www.crystalfontz.com/products/635/CFA_635_1_0.pdf

The module will not draw current from the USB +5v until the OS says it is OK.

 

[omegaman]

Ahhhh...just like the 633 - a separate power feed!
The datasheet should be revised to make this point clearly on page 13 (command 4).

Many Thanks!

 

[omegaman]

One final note. I want the display to power-on when *USB Power is applied* not some external source like +5VSB. This way the unit lights up when the system is turned on.

So I removed the solder from JP2 and then ran a wire from +5v of the USB connector CN3 to the top pad of surface component labeled RC. RC is attached to the same voltage net as +5v on connector H1 which powers the backlight, if not the LCD controller too.

See the attached Jpeg image.

 

[CF Tech]

If the CFA-635 is the only device on a powered hub, or the only device on a motherboard header, this mod will probably work.

For reference: This mod "breaks" USB's power management. For instance, say that a modded CFA-635 (300ma) and another device (400mA) are plugged into a passive hub that can only supply 500mA. The modded CFA-635 will be taking its 300mA from the start. When the OS tells the other device to turn on, then the total current is 700mA, overloading the hub. Sadly, some poor designs (and amazingly . . . even some commercial ones) ignore the power management all together and start drawing power instantly as a module modded this way would.

It is probably fine if the module is plugged directly into the motherboard or a powered hub--where you are basically manually allocating all 500mA to it.

 

[omegaman]

Absolutely correct. Powering the Display from the USB power line prior to device enumeration violates USB design specs.

However, I am attaching the display to an internal port and will be the only device on this hub. So, as you've stated, I will be manually allocating all hub resources to this device.

BTW, how much power does the display claim when enumerated?

 

[CF Tech]

I do not know ho much the module consumes before enumeration. The FTDI chip takes care of all that and (I assume) guarantees that it is all within the USB spec. We use a FET (near zero leakage) to shut off all of the power to the module until the FTDI chip says it is OK to draw power.