I've posted before about this but still haven't figured it out and have some new info. Quick recap, we've designed several of our own boards using Teensy 3.6 design and Arduino, mostly with no issues. One out of every 10 or 15 boards we make does not connect to Windows 10/Arduino right from first power up (no code downloaded). Looking at the reset pin with a scope shows it low for about 75us, then released for about 3us, at which time it goes low again and repeats this cycle. With some boards pressing the program button results in reset high continuously as it should be but the oscillator is not operating and no USB communication (obviously, with no oscillator). On other boards a button press does not change the reset pin behavior. I've tried the 15s button press too - behavior is the same. We've had success in these cases by replacing the processor and/or bootlloader, but obviously that's quite a bit of work even though we use the QFPs. I concluded that there is some corrupt code in the MK66 that is causing it to reset itself almost immediately after coming out of reset (I've cut the reset track to the MK66 and see the same thing, so I know it's the MK66 asserting reset). We do have a voltage monitor on the reset line (MCP130T-270) which holds reset low for ~350ms at power up. I thought that might be interfering with bootloader/MK66 communication at power up but then I read this thread which indicates that it's OK to use a Vcc monitor: https://forum.pjrc.com/threads/53176-Teensy-3-6-Reset-Pin?highlight=15+seconds
I'm pretty confident in our hardware - the Teensy schematic is almost identical and we have ground and power planes, thorough decoupling, very stable 3.3V, etc. Love to hear any thoughts.
Thanks
I'm pretty confident in our hardware - the Teensy schematic is almost identical and we have ground and power planes, thorough decoupling, very stable 3.3V, etc. Love to hear any thoughts.
Thanks