Teensy3 and 3.1: SPI SCK on Pin13 -> May the LED pose a problem at high speed?

[Ben]

Hello everyone, a quick question:

I'd like to use Teensy 3.0 with an SPI-flash at high bus speed. The default pin for SPI clock is Pin 13, which has the Teensy onboard LED attached to it. May this LED pose a capacitive load big enough to degrade the clock signal at high speeds, or am I worrying without any reason?
I'd not bother to ask and just use the alternate clock cin (Pin 14 / A0), but that would substantially complicate my PCB layout, plus I'd loose one analog input and had to start using the SMT-pads on the bottom (A12 and A13).

Ben

 

[Constantin]

What's capacitive about a LED with a resistor? I have not heard of anyone having an issue with this arrangement but I'm happy to be wrong.

FWIW, whenever I'm doing transactions at 20MHz (?) and 1.4ksps on a SPI-interfaced ADC, the light simply looks dim, i.e. It looks like using PWM for brightness control.

 

[PaulStoffregen]

or am I worrying without any reason?

It's really not an issue. At some extremely high frequency, such effects might matter, but that point of far beyond the maximum 24 MHz SPI speed Teensy supports.

Plenty of projects have worked very well, at 24 MHz clock speed, with that LED and even multiple breakout boards plugged into solderless breadboards.