Wireless Tracker - GPS pins BOOT_MODE and D_SEL

Hi folks,

I’ve been staring at the schematic of the Wireless Tracker for quite a while now. Only just now, I noticed that GPIO 47 (BOOT_MODE) and 48 (D_SEL) are actually wired up to the GPS module.
From the schematic, these appear to be pulled up to Vext by default, which is the powersource of the GPS module. Therefore, I expect that setting those pins as OUTPUT/LOW would somehow affect the behaviour of the GPS module.
I tried setting either of them LOW or HIGH before starting the GPS module, but in all four cases, I still get valid GPS output. What is actually the point of these pins? Does anyone have a clue or guess?


It appears that the UC6580 is functionally at least very close to the UC6226. In an old version of that thing’s datasheet (https://docplayer.net/200039602-Ufirebird-uc6226-gnss-positioning-chip-datasheet-specifications-and-features.html) they describe that the BOOT_MODE is used to set the chip in SPI slave mode for firmware upgrades, instead of the default 20ms window available in normal use; the D_SEL pin is used to select SPI or UART/I2C mapping to the chip’s pins.
In the new version (https://en.unicorecomm.com/assets/upload/file/UC6226_Datasheet_EN_R3_81.pdf) the changelog shows that this description is deleted, and only a single mention remains in the pin description. It appears these pins do not do so much for the chip anymore.

But still - the description is not for the UC6580 exactly and I assume there’s a reason the pins are broken out. Soo… anyone got a clue or guess?