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Another TI-85 assembly shell


Mike Baker
Martin Hock


Release Date

August 1, 1997






PhatOS is the latest product in a line of many that exploits a bug in the TI-85 calculator to allow users to run programs written in Z80 assembly
language on it. Unlike preceding products, PhatOS was written to try to bring together shells rather than create potential causes of fragmentation.
As such, the only new feature PhatOS adds to the original ZShell features to the program end is relocation, which is well documented for other shell authors to hopefully emulate. However, PhatOS adds many features to the operating environment end in order to make your calculator experience as phat as possible.

"That's kinda phat, but not really phat," you're probably saying. Ah, but here comes the phat part. Press F3 on a program. Where did it go? Well, you just converted the string into a PhatString. Press F5. Wow, the triangles changed! And there's your program! Well, what's so great about PhatStrings? They do not show up ANYWHERE in the normal TI-OS! Which means that if your teacher tells you to delete your programs, you can proudly show her that there aren't any! Also, you can use it to organize your programs. For example, one type could be games, and the other could be utilities. One could be normal stuff, the other could be sensitive material. It's up to you. Note also that pressing F3 on a PhatString converts it back to a normal string, and pressing F5 while viewing PhatStrings will switch you back to viewing normal strings. It is safe to convert all programs to PhatStrings. The only programs that will probably not work are strings that are called externally by other programs. If after converting one of these strings you find that things don't work, just convert it back. No actual changes are done to the file itself, just to the VAT entry.

ExtraPhat strings/PhatStrings:
Now, there's one more special type of program: the ExtraPhat program. An ExtraPhat program can be a PhatString or a normal string. You'll notice that the ExtraPhat programs are indented a little. What makes them Extra Phat? Well, these programs relocate themselves to a known address in memory ($9000). These programs use absolute rather than relative PROGRAM_ADDR style addressing. In English you say? Basically these programs are about 10% smaller and a little faster than normal ZShell programs. The tradeoff? Only about 90% of all programs can be converted to ExtraPhat programs, and this requires the source code. However, you can find ExtraPhat programs at the PhatOS web site. Also, programs are easily converted to ExtraPhat; it only takes about 10 minutes for the programmer. Bug your favorite ZShell developer today!


Phat OS is yet another "damn shell for the TI-85". Why did we write it then? Well have you ever looked at something and said "I can do better than that!"? Well, that's exactly how we felt. (And besides everyone else had a shell, we didn't want to be left out) Rather than doing things the cshell way and just hexedit a few lines of text (and saying we wrote the thing), we decided it was best to start at the ground and work our way up. Yes this is the hard way of doing it, but we felt it was better than starting with someone else junk, so we pulled out the ol' ushell asm, using it to figure out the proper ways hook a shell in to the os, and still have things work when you quit.With a little bit of work on my half we had our first shell, the mini shell that is packaged with PhatOS. This shell was only the beginning, a sign of things to come. (or in other words "a crappy, yet small shell to test zshell functions")

No Phat shell would be Phat without good features, and we are proud to lack most of em. Why well think about it: Every shell that has come out sofar has added features above and beyond zshell, that's the the marketing catch, but it cause alot of problems; People try to release shells with the "killer feature" a feature so great everyone wants to use the shell, things written for the shell don't work with other things, and basically you've cornered the market and as long as you don't tell anyone how those features work, your shell will remain the best. (this is where the decompile i talked about could come in handy <g>) rather than do that and hope our shell catches on, we decided to limit the features we added (and document them well so any other shell out there could easily add them HINT HINT). Well enough of this, how about listing some features:

Library Support Not Added because it is a waste of space (see readme)
Auto Power Down Automatically shuts off your calc after 5 min or when you press 2nd in the shell
Relocation Moves a program to a certain spot in memory thus eliminating the need for CALL_, JUMP_ and some other stuff (saves around 10% per program)
PhatStrings With the press of a button you can change strings to type20 (a type hidden from ti-os)
ExtraPhat files A new file type, this file is a relocating file wich saves alot of space for you.

Mike Baker:

A semi retired asm programmer and self proclaimed lazy person, I spend my time thinking of useless things yet to be programmed, and trying to convice Martin Hock to program them for me. I'm also the author of Lode Runner the only 'game' i ever made for the 85, and also the first thing I ever did in zshell. (LR has been written "whenever i feel like it" which at rate we should have another version in two or three years ;)

Martin Hock:

Martin Hock is a still-active (single) programmer who's thinking about switching over to x86 assembly and coding some Real games, except for the fact that x86 asm sucks. He spends most of his time getting a CRT tan from either his monitor or his television. He recently moved to Montana which, in his own words, "really sucks, but it's better than cereal."

The Phat Operating System (hereby, heretofore, hereupon, hereinafter, hereinbefore, and hereunto referred to as "PhatOS") and its creators ("Adolescents with nothing better to do") shall not be held responsible for the effects of the use of its product, including but not limited to an increase in phat and free calculator memory.


This Odd End-User License Agreement ("OEULA") is just too phat. If you do not follow it, we reserve the right (at any time) to, at our discretion, castrate or, in the event that you have no testicular sac, severely maim you.

i.) At any given time, you may have 1 (one) (uno) (JUST ONE OF 'EM) cop(ies) of PhatOS (patent pending) on any one Texas Instruments TI-85 calculator. If you copy the string over and over, filling up needless space, you are required by law to put your head in a meat grinder.
NOTE: Texas Instruments is a copyright of Texas Instruments. This organization is not in any way affiliated with the State of Texas, the former Lone Star Republic, anyone nicknamed "Tex", or the creators of PhatOS, nor do they sing the "Happy Trails" theme song while herding cattle.

ii.) It is recommended that you do not upload ("load up") this Phat-OS zip file ("Phile") to any web site that contains pictures of Scully (TM), Mulder (TM), Skuller (NOT TM), Moldy (ALSO NOT TM) or any other character or caricature from The X-Files (TM) representing the creators of the site. (EVEN THE SMOKING MAN) (TM) If you wish to do this, please realize that The X-Files (TM) has NOTHING WHATSOEVER TO DO WITH CALCULATORS and proceed with caution.

iii.) This program may not be sold for profit. If you sell it for profit, please include as a free bonus your internal organs. It also may not be put on any stupid piece of crap sold by NukeWare Inc. ("PukeWare") or any other software company unless they give us a hefty ("Somewhere in the range of 50%") chunk of the profits.

iv.) Employees of Microsoft Incorporated (M$) may not, at any time, use any of the PhatOS code in any current or future operating system, including but not limited to Windows 95, 98, 99, 99 1/2, and especially 00 ("The Number Zero Operating System"). Considering that the code is in Z80 assembly language, this would probably be quite easy, as it has been confirmed that M$ is considering switching to a Z80 emulated virtual machine in the future. (They are gradually moving toward CP/M, which is the true future of computing.)

v.) The use of ebonics in any program designed for PhatOS is prohibited. Violaters are required to watch Mr. T say "Ah pity da foo" repeatedly for at least 5 (five) consecutive hours.

vi.) You may not rent or lease your copy of PhatOS, though it is technically OK to hold it in front of someone's face and taunt them with it.

Under the terms of this license agreement, it is illegal to use this software if you are, represent, work for, or worship any of the following:
1.) Barney the Dinosaur ("B'Harne")
2.) The United States Government and any subsections thereof (including but not limited to the cast of the television show M*A*S*H, disgruntled postal workers, George Bush, and any janitor that washes excrement ("shit") in the government washrooms ("shitholes") )
3.) Anyone in Texas Instruments that opposed the idea of assembly language
4.) The Brady Bunch and any subsections thereof (including but not limited to lovely ladies and very lovely girls with hair of gold, four men living all together yet all alone, and groups with more than a hunch that they must somehow form a family)

Phatsoft Inc. is not affiliated with Philadelphia, "America's Phattest City" ( or "Fran's Phat Ass Homepage" (address withheld)

The use of the word "Phat" in any programs not specifically licensed by the formerly defined "Phat Hackers" is strictly prohibited unless your name is Fran and you are the creator of "Fran's Phat Ass Homepage", in which case you have already suffered enough, as evidenced by your name. We wish to save Fran the embarassment and not state the URL here (and save ourselves some embarassment from pubically admitting that we found it) (Entirely by accident, of course)

Development History

  • A chronological overview of the product's development


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