Strapping pins?

richardax

New member
ESP32 has a few strapping pins that needs to be left alone during boot.

Does Teensy 4.1 have any?

I built a project where I need 100k pullup to pins 30, 31 and 32.
(I cannot use the internal pullup as they are pulled down by 27k and internal is 10k which will not detect low.)

WIthout these resistors there is never any problem uploading without having to push the "upload button".
With the resistors I get error upload and will have to push the button.

Is the external pullup not allowed at these pins?
 
Not seen any notes about pins 30-31-32.
Just wired 3.3V to them here on a T_4.1 and upload has no issue. Using Blink or SDCARD and ListFiles.ino and SerialEvent.ino noted below.

Something else is going on it seems.

Try this example and from SerMon enter text the Teensy will ECHO back to confirm USB is working:
> ...\examples\04.Communication\SerialEvent
If that works add something of the sort to the unshown sketch and confirm USB is working when the attempted Upload fails.

Only pins found to have any signals applied during RED LED bootloader operation are #24 and #25 and they are given 3.3V in some fashion while the RED LED is on.

And just noted if a LOCKED 1062 Teensy is in use and pin #25 is held to GND, then it cannot be programmed, even with the Program(upload) Button.

Not indicated that the Teensy at hand is a 'LOCKED' version, or that pin #25 is held low and the behavior does not match.
 
I built a project where I need 100k pullup to pins 30, 31 and 32.
...
WIthout these resistors there is never any problem uploading without having to push the "upload button".
With the resistors I get error upload and will have to push the button.

I tried but could not reproduce this problem with a Teensy 4.1 and 100K resistors on pins 30, 31, 32. I uploaded the File > Examples > 01.Basics > Blink program many times by clicking Arduino IDE's upload, no need to press Teensy's pushbutton. I even unplugged the USB to power off and then reconnected. I was again able to upload from Arduino IDE without pressing the pushbutton on Teensy. I did at least 10 successful uploads.

I could not reproduce the problem you described. Here is the hardware on my desk, so you can see how I tested.

1711972511177.png


To answer your original question, Teensy 4.1 does not have "strapping pins".

However, the RT1062 chip on Teensy 4.1 does have pins AD_B0_04 and AD_B0_05 which function similar to "strapping pins". These 2 pins of the RT1062 chip are not connected to any of the Teensy 4.1 user accessible pins. AD_B0_04 connects to the bootloader chip. AD_B0_05 is permanently connected to GND. Refer to the Teensy 4.1 schematic for details (scroll down past documents and dimensions to "Schematic").

Also to confirm what Defragster said, there is a known issue with Lockable Teensy when locked into secure mode, where driving pin 25 low prevents entry into bootloader mode, even when pressing the pushbutton. This only applies to Lockable Teensy and can never occur with standard Teensy.
 
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Thanks for the quick replies.

Today I have no problems at all. Yesterday I had problem about 9/10 times. Guess just something weird going on yesterday.

Thanks again. Good to know there are no accessible "strapping pins".
 
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