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What was LCD test mode used for?
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aeTIos


Power User


Joined: 02 Nov 2010
Posts: 491
Posted: 12 Jun 2012 07:07:35 am    Post subject: What was LCD test mode used for?
See topic title. If you can kill the LCD with it, what is the use of a Test mode, and why was it called "test mode"?
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Tari


Systems Integrator


Joined: 03 Jul 2006
Posts: 2107
Location: Always-winter, Michigan
Posted: 12 Jun 2012 07:29:23 am    Post subject:
It's probably used for automated testing of the driver before it leaves the factory. They can instrument the die with a bed of nails, then command the device to enter test mode to exercise all the outputs to their rated limits, flushing out any manufacturing defects before even splitting up the wafer.

Just my guess.
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Travis


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Joined: 03 Feb 2011
Posts: 212
Location: Kansas, USA
Posted: 13 Jun 2012 07:01:01 pm    Post subject:
I've always wondered, has anyone ever actually proven that the LCD can be damaged this way? Or is it just something people assume can happen.
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aeTIos


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Joined: 02 Nov 2010
Posts: 491
Posted: 13 Jun 2012 07:03:44 pm    Post subject:
Yup it is proven.
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Tari


Systems Integrator


Joined: 03 Jul 2006
Posts: 2107
Location: Always-winter, Michigan
Posted: 13 Jun 2012 07:09:12 pm    Post subject:
aeTIos wrote:
Yup it is proven.
[citation needed]

I recall seeing a video a while ago in which the liquid crystal had been 'liberated' from the pixels on an 83+ and merely sloshed around the LCD when it was tilted, allegedly from leaving it in test mode. That seems plausible if we assume the LCD driver is driving the rows unusually high.

If anybody remembers who made that video or even where we could find it again, that would be great.
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shmibs


Advanced Member


Joined: 25 Nov 2009
Posts: 230
Posted: 14 Jun 2012 11:55:32 am    Post subject:
i'd be willing to test it out on a spare, partially-broken calc if you guys really want to know.
how is it initiated?
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ohithur
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aeTIos


Power User


Joined: 02 Nov 2010
Posts: 491
Posted: 14 Jun 2012 12:04:33 pm    Post subject:
initiate it by doing

Code:

(header here)
ld a,($1C)
out ($10),a
ret

or if you don't want to assemble create a program with this:

Code:

AsmPrgm
3E1CD310C9

This will turn test mode on. Be sure to keep your fingers close to the batteries if you don't want to damage your screen too badly.
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KermMartian


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Joined: 14 Mar 2005
Posts: 55736
Location: Earth, Sol, Milky Way
Posted: 14 Jun 2012 12:44:04 pm    Post subject:
Can't you just do it from the MODE-ALPHA-S self-test? Or does that not engage the LCD test mode at any point?
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aeTIos


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Joined: 02 Nov 2010
Posts: 491
Posted: 14 Jun 2012 02:02:55 pm    Post subject:
Nope, afaik not. And that does wipe the whole memory.
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