TI-81 Hardware and ROM Versions

[CVSoft]

As many people know, I have extended my work with documenting the hardware and ROM versions of the TI-82 over to the TI-81, and my current findings are published here. Throughout the research, I purchased three TI-81s: 0719871 I-0790, ROM 1.1; 1210793 I-1292 'B', ROM 1.8K; and 0804828 I-0893 'D', ROM V2.00. I targeted the undumped ROM versions to add to my collection; ROM dumps can be expected in the next few months after this initial posting.

Hardware Versions
There are at least 7 distinct variations of the TI-81, each with a unique external physical appearance:

1. The original TI-81, which began production around the beginning of 1990. As well known, these do not have a backup battery; however, these do not have a bar below the [ON] button. Additionally, the place where the backup battery should be instead contains two plastic rings (see the detailed comparisons below for a picture).
   
2. Still in pre-'A' hardware revisions, the second variant of the TI-81 was introduced in May 1991 to prepare for the implementation of the TI-81 'A' and TI-85. A plastic bar was added below the [ON] button to prevent accidental presses. The backup battery's socket and labeling is present under a flat plastic cover, but there are no contacts under the cover.
   
3. The third variant of the TI-81, hardware revision 'A', added a backup battery. The battery information on the back of the calculator was updated to indicate this.
   
4. The timing coinciding closely with the release of the TI-85, the fourth variant of the TI-81 (hardware revision 'B') drastically improved the quality of the display and changed the texture of the screen cover to the even texture used in all later calculators until the TI-73. The screen was upgraded to one with viewing characteristics quite similar to the TI-85's screen, with blue-on-green pixels and a wider viewing angle. Due to a change in the contrast-setting code, these all have ROM 1.8K. This variant had a long production run, from April 1992 to sometime around May 1993.
   
5. Unfortunately, the fifth variant of the TI-81 undid these improvements. Externally, the most evident change is the housing plastic is no longer a bluish gray but rather a dark blue. The display bezel still uses the style of the TI-85 and variant 4 TI-81s. The mold used is very similar to that of the TI-82, differing only by the missing link port. Internally, this variant (and all future ones) use TI-82 PCBs and display drivers with TI-81 RAM and ROM chips. There are a few other changes, mostly relating to the higher CPU clock (6 MHz vs. 5 MHz) and different RAM/ROM chips. Different pinouts are compensated for by using zero-ohm resistors to connect the correct pins. All TI-81s of this variant that were checked use ROM V2.00.
   
6. Towards the beginning of 1994 or the end of 1993 (I am not certain due to the very poor readability of date codes on the dark plastic TI-81s) the display bezel was restyled to match the TI-82's styling, with the "TI-81" text bolder and to the right, while the TI logo was moved to the far left of the bezel labeling area. Internally, the RAM chip was changed to use a Suwa Seikosha SRM2264 in place of a Sharp LH5160N (due to a very limited sample size, this is not confirmed), and the ROM version was updated to V2.0V.
   
7. At the beginning of 1995, the TI-81, TI-82, and TI-85 all received a cosmetic change to their display bezels. On the TI-81, the display bezel was made much narrower, the background color is the same blue color as the calculator's plastic, and all text is white. "TI-81" is no longer italicized. Internally, the PCB was updated to version 31A (also seen on the TI-82). To my knowledge, no other internal changes were made.
   

	The backup battery area. First variant on left, fourth variant on right.
	The display bezel's reflectiveness can be noted on the leftmost TI-81, first variant. Fourth variant TI-81 on right.
	The display bezels of my TI-81s. Top left is first variant, top right is fourth variant, bottom left is fifth variant, bottom right is sixth variant.
	The bar below the [ON] button is not present on the first variant TI-81 (on left), but is present on the fourth variant TI-81 (on right).
	The added backup battery information is visible on the fourth variant TI-81 (on right).
	The number key font size was increased between March and May 1993.Fourth variant on left, fifth variant on right.

ROM Versions
Nine ROM versions are known, dumped versions are in bold:

• 1.0
• 1.1
• 1.1K
• 1.5K
• 1.6V
• 1.6K
• 1.8K
• V2.00
• V2.0V

Very early TI-81s, along with at least one produced in December 1990, use ROM 1.0. Version 1.1 is uncommon, and is present in both known July 1990-produced TI-81s. Shortly after 1.1, 1.1K was introduced and is common towards the end of 1990. Around March 1991, ROM versions 1.5K and 1.6K were introduced. 1.8K is paired with hardware revision 'B'; V2.00 was introduced when the plastic color changed to dark blue, and V2.0V was introduced alongside the 1993 screen bezel redesign.

[Adriweb]

Lots of nice and detailed info, as usual - good job

[critor]

I agree !

[CVSoft]

I have, through the grace and wonders of Adriweb, acquired a TI-81 with a remarkably low serial number, 0600008 I-0690. June 1990 is the first known month of production, so hopefully something interesting is inside. At the minimum, we should finally get a ROM dump of 1.0. Expected arrival is towards the end of this week. Being just one month older than my 0719871 I-0790 TI-81, I'm not expecting too many differences; however, Datamath's 1st-generation (variants 1 and 2) TI-81 database show that ROM chips for 1.1 appeared in 0790, with 0690 using ROM 1.0.

Analysis of this 0690 TI-81 should provide an accurate production date for the TI-81 variant 1 shown at Datamath. I took a look at the Datamath TI-81 'ES', cross-referencing it against the various EPROM-based TI-82s in my own collection; after carefully analyzing the PCB images, it shows the same type of soldering that I have observed on my TI-82s, specifically at components R11 and C2. The vias near D3, C7, and R11 are tinned, probably to attach wires. Some things observed on the TI-82s are not seen on Datamath's TI-81, such as labeling of the ROM version on the PCB, additional markings on the ICs, or soldering around the ROM chip (there looks to be some stuff on pin 28, but due to lack of resolution I cannot determine if this is actual work or simply a defect in production). If this is indeed a subject of prototyping, then it is a late prototype as the software environment had already been finalized along with the PCB components and layout.

A note for prospective collectors: avoid buying pre-1995 TI graphing calculators missing serial numbers; these are applied on stickers and are frequently peeled off, especially when sourced from ex-school lot sales. Check ROM version if a serial number is missing, and compare physical attributes with the variants above. The older TI-81s are known to use a Toshiba T6A49 ASIC, changing to a T6A49A around 0990. Finally, the earliest of TI-81s will show evidence of soldering around some components.

Note: a four digit number indicates a specific month formatted as a date code, e.g. 0690 --> June 1990. Yes, I've become this lazy.

[Ti64CLi++]

I think I have got a Ti-83 with OS 1.1 or 1.0

[critor]

I think I got a Ti-83 with OS 1.1 or 1.0

TI-83 or TI-83 Plus ?

[Ti64CLi++]

Ooooooooups, I wanted to say TI-81

[critor]

Ok.

Could you please check if it's 1.1 or 1.0 ? The difference is important.
The key combo to display the ROM version is

2ND

TEST

ALPHA

S

.

ROMs 1.1 and 1.1K have already been dumped.
ROM 1.0 is still undumped for now.

[Ti64CLi++]

Tu peux me parler en français
Sinon, je ne l'ai pas là avec moi, mais je te dirai cela demain

[critor]

Super, merci beaucoup à toi.