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TI-81 Screen Types?

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CVSoft:
Browsing around eBay, I noticed that some TI-81s have a screen that is off-white and have bluish-gray pixels, while others have the standard STN screen like a TI-82. Did TI change the screen type?

http://mycalcdb.free.fr/main.php?l=0&id=1842
 vs
http://www.partlancer.com/pics/TI-81-Graphing-Calculator-WORKS-FOR-SCHOOL-LOOK.JPG.jpg

TIfanx1999:
I'm not sure. Ti does change stuff sometimes (ti 82s and ti 83s have different screens on different models).  Sometimess screens just look different due to crummy pictures. You shold check data math and see if they have any info on it.

TravisE:
My understanding from talking with people like Ben Moody, Randy Compton, and Michael Vincent is that some TI-81 units did indeed have a different LCD. I think some of the earliest ones had the high-contrast bluish ones like the 82 and 85, but most of them (like my ROM 2.0V one) had the grayish, poor-contrast version with only ten contrast settings instead of 32. Not sure why they would switch to a worse version unless it was due to cost.

Interestingly, the interface with the LCD changed on some models, too. Apparently early TI-81s had a memory-mapped display like the TI-85 and 86, while the later ones (2.0V and above?) reverted to an 82-style display driver and hacked in an interrupt routine to periodically copy the entire display to the driver. This often results in an odd, slow, flickery effect when running programs that rapidly clear and display text on the screen on these units.

DJ Omnimaga:
Actually the first models had the light gray (hard to see) ones, since I got one of the first models (without the button battery slot). I never got to see a newer one, though. As for memory mapped-ness, I wonder if this is why the Disp command is faster on my TI-81 than the other models?

TravisE:
Perhaps they switched back and forth once or twice, since yours (1.1K or something, IIRC?) and mine (2.0V) have gray LCDs, but I think Randy said his 1.8K model had the blue one.

As for Disp speed, the models with memory-mapped displays would certainly appear faster (or at least, less choppy). I'm not sure if this alone could account for actual speed in terms of lines printed per second, unless the slow copy-to-driver interrupt routine consumes enough time to noticeably slow down everything else (which it may or may not, I don't know).

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