Teensy 4.1 SPI SCK pin13 (LED) issue

clappertown

New member
Hi,

I have a project that has to use both SPI and LED functions on Teensy 4.1 ( I already used SPI1, and SPI2 pins at back side seems not easily accessible). Based on front side pin layout, it seems pin 13 is used for both SPI and LED, and there is no extra pin can be used for SCK. This is different than Teensy 3.5/3.6 where I can use pin 14 as an alternative pin for SCK. So my question is that if there exists other pins that I can use as SCK, other than pin 13 (LED) ?

Thanks.
 
Referencing the T_4.1 card there is a single instance shown for the SPI signal SCK and that is pin #13. No ALT pins in a grayed for that signal.

Alternative would be to wire to any other pin an LED and proper resistor to get the LED feature that is tied to pin #13.

{testing}
 
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I have wondered whether an SD card extension cable like this could be butchered to bring out the SPI2 pins (SCK2, CS2, MOSI2, MISO2) without having to solder onto the QSPI memory pads. Anyone tried that?
 
Perhaps such a PCB?

Adapter.jpg

Paul
 
Looks good.

No matter which kind of cable or PCB is used, be careful about the total power supply capacitance if it will ever be hot plugged. The Teensy 4.1 design assumes a SD card with very little capacitance. If you have several uF power supply decoupling that's discharged and you hot plug, you could end up creating a 3.3V power brown-out condition that crashes Teensy 4.1. The bootloader chip implements brown-out detection, so the hardware should automatically reboot. While that's better than just getting stuck without recovery, still probably not what you want to see when plugging in the cable.
 
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