Reset pad; Program button...

[kenhorner]

I'm curious as to the difference in the Program push button and the Reset pad on the bottom of the 3.2 unit. Are these explained in any documentation? Searching the Forum doesn't turn up much useful info.

For example, if I were to use the Program pin as a Reset line for other circuits, would it also restart the code on the Teensy? --as the Reset pin on an Arduino would. I'm going to put this Teensy into a closed case and will be unable to push the button. So I'm going to run a wire from the Program pin to an external accessible switch. Do I need to also connect to the Reset pad with another switch?

Thanks.

 

[drmartin]

The Program Push Button halts your program and starts a special bootloader program. The Teensy then waits for the Teensy Loader utility on your development system to upload a new program.

Pushing the Program Push Button without the Teensy Loader utility running on your development system results in an infinite wait with the Teensy waiting for a new program to be uploaded over the USB connection. You have to power cycle the Teensy to abort the "wait for new program" mode and restart your old program from flash in the Teensy.

Most people simply depend on a power cycle to restart their program if needed.

The Reset Pad on the bottom of the Teensy 3.2 provides a more conventional Reset Function. It just restarts the main microprocessor on the Teensy board and does NOT invoke the bootloader mode. The Reset Pad provides a way to restart your program without needing to power cycle the Teensy board.

NOTE: The Reset Pin of the microprocessor is bidirectional wherein certain internal modules can create a reset pulse on the Reset Pin. Examples could be internal watchdog or internal Power Fail detect. I mention this because excessive external load on the Reset Pin can affect the ability of the microprocessor to properly respond to internal reset sources.

See the Teensy Schematic at
http://www.pjrc.com/teensy/schematic.html
for details on the Program Pushbutton vs the Reset Pad.

Generally speaking the USB Driver inside the Teensy can detect and respond to the Teensy Loader attempting to upload a new program without the need to push the Program Pushbutton. However, the world is not perfect and occasionally it is necessary to use the Program Pushbutton to get a seriously lost Teensy back into bootloader mode. I'll bet I have pushed the Program Button twice in the last year....

 

[kenhorner]

Thanks for the prompt response. In the experiments I've been doing, I concluded that the situation might be as you described. Now I've got several good avenues to pursue. Cutting power to just the CPU and leaving other things running might work. But I think the reset pad maybe with a diode to avoid loading it maybe the best approach. Thanks much.