Keyboard/Joystick conflict

[Tursi]

I ran into this recently and spent some time investigating it... basically, if a key on a keyboard column shared with the joystick is pressed, the joystick axis does not respond (only the key is read).

 

Basically, this means that:

- FCTN,1,2,3,4,5 - and Alpha Lock - will disable UP

- 6,7,8,9,0 will disable DOWN

- Enter,O,I,U,Y,P will disable RIGHT

- Space,L,K,J,H,; will disable LEFT

and =,comma,period,M,N,/ will disable FIRE

 

As far as I can work out, this is because the keyboard lines are directly connected to the 9901, but the joystick lines run through protection diodes. So if a key is pressed it's basically going to sink all the current rather than pushing through the diode.

 

Since it's hardware, you can see it regardless of the software. I was able to reproduce it in TI BASIC as well as my own software. Any game should show it too, doesn't matter if it means to read the keyboard or not.

 

I was trying to use the joystick as a modifier for keypresses, copying code I used on the ColecoVision, and it took a while to figure out why UP+1 wasn't working...

 

I'll add that discovery to Classic99 as well so it doesn't trip me up in the future, but I thought I'd share it in case the others didn't already know!

 

Edited April 27 by Tursi

[Gary from OPA]

It would be nice someday to restore the joystick back to how it was originally going to be with variable degrees when ti was working on the keypad round wheel via rf or ir transmitter/receiver with the values being returned from +16 to -16 instead of just fixed at +4 and -4 and 4 player option

Edited April 27 by Gary from OPA

[+OLD CS1]

29 minutes ago, Gary from OPA said:

It would be nice someday to restore the joystick back to how it was originally going to be with variable degrees when ti was working on the keypad round wheel via rf or ir transmitter/receiver with the values being returned from +16 to -16 instead of just fixed at +4 and -4 and 4 player option

Considering how poorly variable joysticks were implemented at the time (self-centering, my ass,) I am happy for what we got.

[Tursi]

39 minutes ago, Gary from OPA said:

It would be nice someday to restore the joystick back to how it was originally going to be with variable degrees when ti was working on the keypad round wheel via rf or ir transmitter/receiver with the values being returned from +16 to -16 instead of just fixed at +4 and -4 and 4 player option

I think that's the first proper pic I've seen of it... nice.

[+mizapf]

9 hours ago, Tursi said:

I ran into this recently and spent some time investigating it... basically, if a key on a keyboard column shared with the joystick is pressed, the joystick axis does not respond (only the key is read).

Yes, I also expected that when I learned why this AlphaLock / Joystick-up problem occurs. So you tested it on real hardware? I'd like to add that to the TI emulation in MAME, but I cannot test for myself.

[Tursi]

2 hours ago, mizapf said:

Yes, I also expected that when I learned why this AlphaLock / Joystick-up problem occurs. So you tested it on real hardware? I'd like to add that to the TI emulation in MAME, but I cannot test for myself.

Yeah, it makes perfect sense now that I know what it is. I tested every combination on hardware here last night, using several pieces of software to make sure it wasn't just software.

[Tursi]

I don't know if the joystick circuit is different on the QI... but I reckon if the Alpha Lock issue still exists there, this likely holds true.

 

[Gary from OPA]

36 minutes ago, Tursi said:

I don't know if the joystick circuit is different on the QI... but I reckon if the Alpha Lock issue still exists there, this likely holds true.

 

I have a QI and somewhere in my junk drawer I have a pair of original ti joysticks. Send me a simple test program and I can try it out.

[Asmusr]

If you use original TI joysticks you would need 3 hands in order to press a key on the keyboard at the same time. 🙂

[Tursi]

1 hour ago, Gary from OPA said:

I have a QI and somewhere in my junk drawer I have a pair of original ti joysticks. Send me a simple test program and I can try it out.

Don't need to! Load any software, or run something in TI BASIC. It's hardware, so the joystick will cut out when you press one of the related keys.

 

10 CALL KEY(0,K,S)
20 CALL JOYST(1,X,Y)
30 PRINT K;X;Y
40 GOTO 10

 

[PeteE]

Does this apply to both joysticks?

[Tursi]

1 hour ago, PeteE said:

Does this apply to both joysticks?

Yes, they run through the same return lines.

 

[jrhodes]

I'm guessing MBX joysticks would also be effected too?

[+OLD CS1]

1 hour ago, jrhodes said:

I'm guessing MBX joysticks would also be effected too?

This probably has implications on the MBX communicating with the TI on the whole, since it uses the joystick port for data.

[Tursi]

I'd agree with OLD CS1, but I've no idea what the implications are.

 

[+FALCOR4]

Let me see if I can get this link to work. 

 

This might be useful to you, KeyBits lets you see the keyboard/joystick interactions directly:

 

 

Sometimes you may want to scan a key or two directly from the keyboard in your software rather than going through the TI KSCAN routine.  This routine, that loads into cartridge ROM, is a quick and easy way to identify the key column and row that you can use for directly addressing the TMS9901.  Also see Thierry's page on the TI keyboard implementation for a good rundown on how it works.  Just another tool in the tool set.   And, yes, the columns are listed vertically and the rows are listed horizontally ?

 

 

KBCART.bin1.49 kB · 65 downloads

KEYBITs.pdf555.88 kB · 73 downloads

[Tursi]

Cute tool! Would have been nice when I was building Classic99.

 

These days if I'm checking one key I don't generally store all 8 bits anymore. It's harder to track which bit to set, but since you usually need to change R12 anyway, you can go direct to the bit you want and save a few cycles. (Very few, true, but still )

 

[+FALCOR4]

I used a simpler version of it BITD to sort out some three-keypress sequences that were misbehaving.  It's also interesting to see some of the differences between the old console and the QI; especially when it comes to the joysticks.