Undocumented feature of TI-83+ (84+ etc) OS.
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I seem to have found an undocumented 'key' on the TI-83/84+ that allows a backspace with the click of one button. It has to be entered via the remote control key method, but it results in exactly a backspace.

I asked in this forum about Backspace on these calculators earlier this week, and no-one said it was possible, so I also assume that this feature was unknown, as well as being undocumented.

I made a longer than necessary video about it and share the details in it. If there is some info I can help someone to understand, please let me know and I will update it.

Oh, and if this is not as it seems to me, then please go easy on me, haha.

https://youtu.be/14MzEwNMNrM
For convenience, the code linked from the video:

Code:
;RemoteControl 1.0
;Remote control another ti83+ over the link port with this
;program.

;By David Lindström okvin@tiscali.se
;http://cirrus.tigalaxy.com
;amended by matalog to demonstrate Backspace remote 'keypress'.

.nolist
.binarymode TI8X
#include "ti83plus.inc"
.list
    .org usermem-2
    .db $BB,$6D
 
loop
 b_call(_getkey)
 ld a,33
 push af
 ld a,$83
 b_call(_sendabyte)
 ld a,$87   
 b_call(_sendabyte)   
 pop af
 b_call(_sendabyte)
 xor a
 b_call(_sendabyte)
 ld hl,flags+onflags
 bit oninterrupt,(hl)
 jr z,loop
 res oninterrupt,(hl)
 ret

.end


The keycode of interest is 0x21, which doesn't have an equate in ti83plus.inc (alongside 0x22 through 0x24).

I assume this is used for the TI-Keyboard, which confusingly has a backspace but no delete key and a delete key in a weird place.
タリ ·· Ask questions the smart way ·· digipres.club
The TI-Keyboard had a backspace???

I don't have one, and tried to recreate one, and found this undocumented ability to backspace!

Are you serious? The TI-Keyboard has backspace? Can you show a video of it? Or something to convince me that it exists on the Ti-Keyboard?

Apparently the TI-Keyboard even used a different language.
I'm pretty sure that it works on most keyboards (Not just the TI-Keyboard), though I could be wrong. Here's a quick test with my TI-84 Plus CE:


However, it could just be that that's on the CE. I'm not sure if it works on older models as well.

Tari wrote:
For convenience, the code linked from the video:

Code:
;RemoteControl 1.0
;Remote control another ti83+ over the link port with this
;program.

;By David Lindström okvin@tiscali.se
;http://cirrus.tigalaxy.com
;amended by matalog to demonstrate Backspace remote 'keypress'.

.nolist
.binarymode TI8X
#include "ti83plus.inc"
.list
    .org usermem-2
    .db $BB,$6D
 
loop
 b_call(_getkey)
 ld a,33
 push af
 ld a,$83
 b_call(_sendabyte)
 ld a,$87   
 b_call(_sendabyte)   
 pop af
 b_call(_sendabyte)
 xor a
 b_call(_sendabyte)
 ld hl,flags+onflags
 bit oninterrupt,(hl)
 jr z,loop
 res oninterrupt,(hl)
 ret

.end


The keycode of interest is 0x21, which doesn't have an equate in ti83plus.inc (alongside 0x22 through 0x24).

I assume this is used for the TI-Keyboard, which confusingly has a backspace but no delete key and a delete key in a weird place.


The TI Keyboard used a different communication method, as shown here from its technical manual https://www.cemetech.net/downloads/files/2043/x2141


The scan codes it uses are also different, as you can see, 21h for it, should produce a 6, not a backspace.




So, it could not be the TI Keyboard backspace that this is using. And seems to be an undocumented feature of the Remote Control link.
  
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