[Coco] CoCo 1/2 arrow keys versus CoCo 3 arrow keys

[Rob Rosenbrock]

There were no diodes on the CoCo keyboard? Makes sense on the membrane keyboards. I guess I never thought about it. I thought I saw them on the CoCo1 keyboard, though.

I’m repairing synthesizers these days, and matrixes play a large part in them, so I find this interesting since my memory of the TRS-80 is something that I do think back to. Every button is in a matrix, and the keys are in their own. (12 columns!) In order to play a chord, several keys will be pressed, (each with a diode,) so there can be no confusion over which keys are pressed. I will read your post.

From my understanding, the keyscan routine would set one row to high with the rest set to low. Then you would read the byte across the columns. A one in any bit would correspond to the key in that row. Then proceed to the next row. Without diodes, I think you could create a circuit through the keyboard that would short one column with another if enough keys were pressed...

> On Jan 14, 2023, at 3:41 PM, Allen Huffman via Coco <coco at maltedmedia.com> wrote:
> 
>> On Jan 14, 2023, at 2:30 PM, Ciaran Anscomb via Coco <coco at maltedmedia.com> wrote:
>> 
>> You gotta be pretty careful about what keys you assign when there are
>> multiple players.  The non-dioded keyboards mean multiple keypresses
>> can "ghost" - when there are two players, if you don't pick your keys
>> carefully, one player may interfer with another.
> 
> Is that from the keyboard matrix? I don’t think I knew about that, back then, but I learned when I was diving in to how to read the keyboard faster in BASIC. I noticed they made sure SPACE and ARROWS were different, perfect for cursor control and games.
> 
> For those who haven’t looked at it, the CoCo keyboard is a matrix. Suppose you have an 8X8 grid, and each square represents a key on the keyboard.  Any key in the same column or row will set that row or column. You can’t tell which key in the column is set, just that one is set. Thus, any keys that are on the same row/column cannot be used with other keys on the same row/column at the same time.
> 
> I drew it out on a blog post back then:
> 
> https://subethasoftware.com/2020/12/09/benchmarking-the-coco-keyboard-part-1/
> 
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