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I have been working my way up the tree of TI graphing calculator knowledge for a few years now and have arrived at the TI-80 branch. Unlike many other branches on this tree such as the TI-82, this branch has gotten no love for the last 25 years, and its about time somebody actually cared about it a little. I have gathered a bunch of TI-80s and in doing so, I hope to add a couple leaves to the branch.

The TI-80 has 3 known hardware revisions (A, B and C). All viewscreen models found to date have had revision C, however, TI has been known to turn very early production models into viewscreens Therefore, it is expected that revisions A and B should also exist as viewscreen variants, but this has not been observed as of now. Here is the information regarding production dates of the 3 known revisions for the non-viewscreen variant:
    Revision A was produced between February 1995 and April 1995, with the vast majority being produced after February.
    Revision B was produced only during May 1995. It is not know whether there are some 'A's and 'C's that overlap into the month of May, but none have been found.
    Revision C was produced from June 1995 until the end of production in late 2000, with the latest known one being manufactured in October 2000

When it comes to the ROM revisions, only 2 are known, 3.0 which is paired with hardware revision A, and 4.0, which is found in the two other revisions. ROM revisions 1.0 and 2.0 have never been observed, and are assumed to not exist in mass production.
Interestingly, 32kb of the usable code of the ROM is contained in the ROM chip, and 16kb is contained in the ASIC, both of which are proprietary. Back in 2010 and 2011, some crazy attempts by Critor had led to 97% of ROM 4.0 and 66.7% of ROM 3.0 being dumped by soldering the ROM chip onto an EPROM programmer to get the contents of the ROM chip, and making the calculator display the contents of its memory on the screen to get the section stored on the T6M53A proprietary CPU. All these attempts were scrapped because Randy Compton (TI-Planet member) managed to write an ASM program to transfer the contents of the ROM from the jack on a viewscreen model. He was able to dump the entire ROM and subsequently create a TI-80 emulator. This has not been done with ROM 3.0 yet, but doing this would require a viewscreen model with hardware revision A since this is the only version that has ROM 3.0, however this has not been spotted and is only assumed to exist.

The main board for the non-viewscreen and viewscreen models is the same except that the communication circuit is not populated on the non-viewscreen model, and the jack is of course removed. Therefore, I believe someone with sufficient skill could manually transfer the components from a donor viewscreen onto a non-viewscreen with ROM 3.0, effectively turning it into a franken-viewscreen. Such a calculator could then in theory be dumped using the same method used for ROM 4.0, resulting in a dump of ROM 3.0. Of course, this would require sacrificing a viewscreen TI-80, which is strikingly rare just for a chance at dumping 3.0.

I own multiple of each revision, along with the latest known one, therefore, I decided to document the hardware.
Here is a picture containing the 4 calculators.

(top left→I-1000C, top right→I-00595B, bottom left→I-0695C, bottom right→I-0495A)

Last night, me and CVSoft/notipa sat down on HCWP to document revisions A through C.

In total, I took apart 4 calculators (one for each revision and the one from 1000 since it is significantly newer than the others)
All 4 had T6A79 display drivers, and a change in the display driver revision does not seem to constitute a large enough change to warrant a hardware revision change, because multiple different display driver revisions have been observed within the same hardware revisions.
Here are the results of what was observed in each calculator.

Factory: I
Datecode: 0495
Hardware Revision: A
ROM: 3.0
LCD Driver Version: 5B
CPU: T6M53
CPU Datecode: 9505H
ROM Datecode: 9504D
RAM: SRM2264LM10 F4Y1 129
Board Datecode: 9512

Factory: I
Datecode: 0595
Hardware Revision: B
ROM: 4.0
LCD Driver Version: 5D
CPU Datecode: 9515H
ROM Datecode:9510D
RAM: SRM2264LM10 F541 236
Board Datecode: 9512

Factory: I
Datecode: 0695
Hardware Revision: C
ROM: 4.0
LCD Driver Version: 5D
CPU Datecode: 9516H
MB: APLMB-30F 2-1
ROM: LH5359NN-80
ROM Datecode: 9516D
RAM: SRM2264LM10 F541 153
Board Datecode: 9509

Factory: I
Datecode: 1000
Hardware Revision: C
ROM: 4.0
LCD Driver Version: 0E
CPU Datecode: 0002
ROM: LH5359NN-80
ROM Datecode: 0008D
RAM: SRM2264LM10 F00212437
Board Datecode: 0015

It is important to note that the datecodes on the ROM, CPU and board are in YY/WW format, while the one on the back of the calculator is in MM/YY format.

On August 14th 2016, an ifixit tutorial about replacing a TI-80's motherboard and screen was discovered by Adriweb. It had been posted in early 2015. The images were not of high enough quality to make out the numbers on the chips, but the board number (TIAPLMB-31G) could be seen quite clearly. Here is the best image from the video:

That board number had not been spotted before and remained a mystery for a few years, but as it turns out, my latest TI-80 (the last one in the list of components) has that exact board number. Taking it apart, I did not notice any difference aside from the board number itself and the type of screws used.

Between revisions A and B, the CPU changed from a Toshiba T6M53 to a T6M53A. The ROM revision changed from 3.0 to 4.0 and the ROM chip went from LH5359NK to LH5359NN.
Between revisions B and C, the ROM chip went from LH5359NN to LH5359NN-80, and the board number changed from APLMB-30F to APLMB-30F 2-1. APLMB-30F-A2-4 has also been spotted in another revision C.
Between early and late revision C, the screws on the outside of the case changed from cross head screws to torx head screws. Inside, only the board number appears to have changed to TIAPLMB-31G.
Thank you very much @mr womp womp for your interest in the TI-80 and your very accurate and comprehensive post about what it is and what has been achieved.

I hope you'll manage to dump the missing third of ROM 3.0 while there are still working TI-80 out there, by transferring their link port or some other way.

Another way could be to film the screen while it is printing the ROM content and then OCR the resulting video, like it has been done with many TI-81 ROM versions. But the much lower TI-80 screen is likely to be an issue...

In all cases, thank you very much for your efforts at archiving and preserving Texas Instruments calculators history.
I'm not sure I'm willing to have a go at it. I think if I had a viewscreen TI-80, I wouldn't have the guts to start ripping components out of it Laughing
If a viewscreen with revision A is found, then it will be a different story, so maybe waiting is the right thing to do for now and if eventually it looks like we aren't going to find one, then we'll see.
Also, for OCR, its been attempted before but the atrocious screen res, coupled with the fact that some characters can't be displayed means that it doesn't really work well enough to be able to extract the whole thing.
From what I could see in soon 10 years, TI-80 VSC are very rare, rarer than other TI teacher calculators and than some TI calculator prototypes.

Maybe because the TI-80 was discontinued after just 2 years, maybe because teachers preferred buying TI-82VSC or TI-83VSC.
Indeed, TI-82/83VSC could also be used to show things to students using the TI-80, with a better display.
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