Hello NicacioY,
It’s something that confused me a bit before, prior to reading this https://forums.raspberrypi.com/viewtopic.php?t=217967 that explains that there are two UART interfaces on a Raspberry Pi: a “mini” UART, and a “full” UART.
- On the Raspberry Pi models with BCM2837B0, the mini UART is usually designated as
ttyS0. - The full UART, also known as the PL011 UART, is designated as
ttyAMA0.
As far as I understand, by default, Bluetooth typically uses the mini UART (ttyS0) on the Raspberry Pi 3 models, which includes the one you mentioned (BCM2837B0). The full UART (ttyAMA0), instead, is usually free and can be used for other purposes like connecting a GPS module.
I don’t know if anyone on the community has attempted to do this except for this topic that may be relevant: Connecting GPS PPS output directly to GPIO thru Shake board - #3 by jason.wood
And, if you need a reminder on how we use the Pi GPIO pins, you can find it here: Technical Specifications