Teensy JTAG Bootloader probing

[Stewieman01]

What should i see when i probe my bootloader on my Custom teensy 4.1 Design? the blink sketch flashes but the USB descriptor fails so i cant program it at all. i have broken out the JTAG pins for the bootloader on my board and wanted to understand what i should be seeing to pinpoint my problem?

when the bootloader button is pressed its LED goes dim and blinks once a second repeatedly which i imagine is it not receiving a signal from the MCU but i cant say.

 

[kd5rxt-mark]

Towards the bottom of <this> page, you'll find a description of how the bootloader process works.

Hope that helps . . .

Mark J Culross
KD5RXT

 

[PaulStoffregen]

when the bootloader button is pressed its LED goes dim and blinks once a second repeatedly

This slow and steady (appox 50%) blink on the red LED (connected to the bootloader chip, not pin 13) means the bootloader is running but it has not heard any USB communication. For a known good Teensy, this blink almost always means you have a power-only USB cable. For a custom PCB, usually it means you have something wired wrong with the USB lines or USB connector.

The good news is if you're getting this blink on a custom PCB, it almost certainly means the JTAG signals are connected properly. The problem is virtually certain to be with the USB D+ & D- signals.