Talk:83Plus:Ports:01

reset needed

From my experimentation with PindurTI, it seems to me that it is impossible to poll more than one group without reseting the keyport in betweeen. Being that I have never tested any direct key input routines. I know the directin routine from MirageOS resets before polling, and LearnAsm28d merely says that one "should" reset the port before switching groups. I hesitate to add this to the comments section without further confirmation. Saibot84 21:48, 1 June 2007 (PDT)

Well, for one 28days is not the best reference for hardware. And pindur is an emulator, so it has the limitations of the PC hardware and what CoBB was willing to put in. However, I decided to check this more since some people keep bringing it up. I have to say my result is not what I expected. It seems that it's possible that groups not even being monitored can affect what is read. I wrote this test program: Link for download. It checks the top row and the arrow group.

Actually being pressed	Arrow	Top Row	Setting arrow without reset	Both arrow and top row
Down	11111110	11111111	11111110	11111110
Zoom & Graph	11111111	11111010	11111111	11111010
Zoom & Graph & Down	11111010	11111010	11111010	11111010
Down & 0 & Sin	11011110	11111111	11011110	11011110
Down & sin	11111110	11111111	11111110	11111110

It seems to be a bug in hardware, dealing with when multiple keys are being pressed. It looks like the AND logic doesn't exists as much as we all thought before. Still though TI set the convention of reseting the key port, but they do it following reads, that may have an impact on the results. Though we still need more confirmation, I tested this with an 83+, 83+SE and 84+SE. --Jim e 09:14, 2 June 2007 (PDT)