1.723V on GPIO and muxing pins

[uptide]

Hello,

Just wondering a few questions about the 3.6,

On page 221 of the manual K66P144M180SF5RMV2 under the pin mux (multiplexing) control it says under 010 through 111 "chip-specific". Does anyone know where we can find what these map to for the teensy 3.6?

Second equestrian, I have pin 13 on the teensy 3.6 configured to mux 001 (it says gpio), high drive strength, and a pullup resistor. (set memory 0x4004B014 to 0b101000011 according to 12.5.1 in the manual). The pin reads 1.723v across pins 13, and ground. changing the mux to 000 changes the potential to .02v

When I disassemble the example blink program there is no reference to this address, so I might be going down the wrong path. The assembly is pretty long and has some neat comments in it, but I'm not seeing where they configure the pins or muxing.

 

[KurtE]

The MUX is set per IO pins...

If you look at the Electrical PDF for the T3.6: https://www.pjrc.com/teensy/K66P144M180SF5V2.pdf
At section 5.1

You will see the muxing for the different pins of these processor chips. You then need to look for example for Teensy Pin 13 which if you look at the Schematic or in the code base or... You will see that this is pin PTC5/LLWU_P9... You then search through that table in the manual to see what the different features are for that specific pin.

Which from my Excel spreadsheet I made during the Beta for the board for pin 13 I see:
ALT0 ALT1 ALT2 ALT3 ALT4 ALT5 ALT6 ALT7
13 PTC5/LLWU_P9 DISABLED PTC5/LLWU_P9 SPI0_SCK LPTMR0_ALT2 I2S0_RXD0 FB_AD10/SDRAM_A18 CMP0_OUT FTM0_CH2

Remember that Pin 13 has an LED connected to it, so it will behave different than most other IO pins.

 

[uptide]

You will see that this is pin PTC5/LLWU_P9...

I set pin for ALT1 (PTC5/LLWU_P9)

I'm wondering, since I don't have an oscilloscope, if the pin is just pulsing the clock at 3.3v at the 180MHz? It would be faster than my voltmeter's sampling rate, how could I test this? maybe put the voltmeter into AC mode?

 

[Theremingenieur]

Since you configured the pin with an internal pull-up resistor and there is another resistor connected in series with an LED from outside, it would be normal to find a voltage which is only a little higher than the LEDs forward voltage as long as the output N-MOSFET in open drain configuration isn’t pulling it down to GND. You might unsolder the LED and find that without that load, the internal pull-up resistor will bring the pin close to 3.3V.