Author: willrandship
Posted: 26 Nov 2012 12:33:30 am (GMT -5)
*All pin numbers are based upon the PCB's silkscreen inside the keypads.
Kerm, about the pins for keypad detection, I'm positive it's not 3-18, since they're the IO pins used to detect keys. I'm also fairly sure about 1 and 2 being just a vcc and gnd source.
If I had to place a bet, it would be on 26, since it's the only pin that wouldn't be used for an input key OR the link port wires OR the i2c touchpad that still goes HIGH on probing. My scope readings say it's held high, so I suspect it's an input with a pullup resistor like all the keys have. However, the rest (27-30) are also potential suspects, since it may be that the 84+ keypad chooses to pull one down and leave one floating, and the nspire swap them. Check to see if the nspire readings match up with the 84+ pad readings for those pins (in the link below) and we'll know for sure.
Unfortunately I no longer have my nspire (it has since become my sister's calculator) so I can't confirm any of it.
I find it interesting how they got keypad input. They had a matrix of inputs tied to outputs, such that they would test for all the inputs with each output separately, AFAICT. This is why in this post I reported square wave readings when buttons were pressed. When it was being polled it dropped to ground, but when it wasn't, pullup resistors brought it back up.
_________________
Hmm...what to put here....
![]()
Posted: 26 Nov 2012 12:33:30 am (GMT -5)
*All pin numbers are based upon the PCB's silkscreen inside the keypads.
Kerm, about the pins for keypad detection, I'm positive it's not 3-18, since they're the IO pins used to detect keys. I'm also fairly sure about 1 and 2 being just a vcc and gnd source.
If I had to place a bet, it would be on 26, since it's the only pin that wouldn't be used for an input key OR the link port wires OR the i2c touchpad that still goes HIGH on probing. My scope readings say it's held high, so I suspect it's an input with a pullup resistor like all the keys have. However, the rest (27-30) are also potential suspects, since it may be that the 84+ keypad chooses to pull one down and leave one floating, and the nspire swap them. Check to see if the nspire readings match up with the 84+ pad readings for those pins (in the link below) and we'll know for sure.
Unfortunately I no longer have my nspire (it has since become my sister's calculator) so I can't confirm any of it.
I find it interesting how they got keypad input. They had a matrix of inputs tied to outputs, such that they would test for all the inputs with each output separately, AFAICT. This is why in this post I reported square wave readings when buttons were pressed. When it was being polled it dropped to ground, but when it wasn't, pullup resistors brought it back up.
_________________
Hmm...what to put here....
