I recently gave a friend my sister's old TI-84+ for his TI-81 (only took that so I had one to give to another person if they needed it). I've decided I want to try to mod it, but I don't know where to begin. What kinds of stuff should I add? What do I take away? And how the heck do I do any of it?

Well, it lacks a link port, so you can't do anything like sound or controlled hardware. Possibilities:

(1) LCD backlighting
(2) Case modding
(3) Power modding (AAs? USB power? Rechargeable/Li-Poly?)
(4) Tap into the system bus and add a link port!

You could dump the ROM from it and use it in Emu8x. I don't know how to do that, but I believe BrandonW and a few other people have done it before.

Well, it's more of an external hardware modification option, but you could build a robot to type programs in for you!

That way you could feed some computer-side software a .81 file (that is, a text file containing the 81 commands, as are found in the ticalc.org 81 section), and then the robot would press the buttons.

Though hacking in a link port would be a much better soution, I swear I recall a discussion somewhere about how it would probably not be possible. Not sure if it was in IRC or on a forum somewhere (UTI, maybe).

It seems to me that since it lacks a link port, you'd have to type in an ASM program to dump the ROM 128 bytes at a time to the LCD, and then manually copy those out. Or I guess you could write image processing software to capture each screenful and OCR. That sounds kinda cool, actually...

That's what Ben Moody did, IIRC—wrote a program to dump the ROM to the screen as a scrolling series of characters, then wrote a primitive OCR program to extract them from a video recording transferred into the computer. I managed to get a ROM dump of my own TI-81 using his program, but it was a huge pain getting the lighting, alignment, etc. just right, and even then I had to take a chance and do a little hacking. It was probably just sheer luck that I managed to get a valid image whose MD5sum matched his.

Ooooh, maybe that's where I came up with the idea; I'm just remembering seeing the ticalc.org news article about that. And here I thought I was being original and creative.

I was interested in doing this, any instructions on how to do so? Particularly on the old hardware version, which is what I have.

I am not sure if it works on older versions. I do know that the ROM 2.0V versions have the solder pads for the link port because they are on TI-82 mainboards. They do have port 7 for the link port.

Darn. Well, on the subject of calc modding, is there an asm way to map some unused space to RAM? I'm pretty sure memory bank B is not used by the TI-81 OS.

I believe that the TI-81's RAM has already been mapped, but I don't know enough Asm to know if this is what you are looking for (and probably isn't). http://www.ticalc.org/archives/files/fileinfo/372/37208.html

This is what I was talking about, found it in the unity.zip file on ticalc. The only problem is, I have no idea how to map a memory bank to RAM.

I don't know that the 81 even has any additional RAM (if it did, there'd be enough room for up to 24k or so more without needing to bank-switch at all). It seems unlikely, but wouldn't hurt to try. Note that that port only applies to earlier 81s, though; later ones (ROM versions >=2.0?) have a totally different hardware design and port mapping.

The newer ones are based on TI-82s, using different chips on the same mainboard. I believe port mapping is the same as the TI-82 on the new ones. It does mention that in the unity.zip files.

I have the 1.6k ROM version, so the port does apply. Could anyone point me to some info on port mapping?

You can use the Unity.zip info. It lists port information for both versions of the TI-81.

I know the info is there, but I still don't know how to map a port. I was looking for maybe some example code, or a brief explanation. (I'm not even really sure if port mapping is a hardware or software kind of thing)

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I meant that I need to know how to map a port to RAM, and adress it, and all those sorts of things.