ESP32 I²C Sending PAIR Command to LC76G AB Module Fails

IoT Modules GNSS Module
1

Hi ,

I’m working with an LC76G AB GNSS module connected to an ESP32 via I²C. The PCB is already fixed, but the module doesn’t have a continuous backup power (V_BCKP). When the ESP32 5V supply is removed and re-applied, the GPS loses power and always performs a cold start, which takes a long time to get a fix.

I want to implement a software-assisted warm start without modifying the PCB:

  • The ESP32 can store the last known UTC time and approximate position (lat/lon/alt) in flash.
  • On module power-up, I plan to send this stored data to the GNSS using the proprietary $PAIR064 command (Set Time/Position) to speed up TTFF.

I already have code to read NMEA sentences over I²C and parse time/position, and I can construct the $PAIR064 command. But when I try sending it, I get:

Injecting Assist: $PAIR064,20251003T103000,6.927079,79.861244,10.0*41
Assist injection failed
  1. Is it possible to achieve a hot/warm start this way without VBAT backup?
  2. Are there limitations sending long PAIR commands over I²C? Should the payload be split?
  3. Any recommended method to reliably inject time/position assistance for LC76G over I²C without modifying the PCB?
2

Hello, the airoha chip can achieve a cold_ fix in 26s (but with a good antenna!), there are some agnss for f.ttf but need to inject…
the pair064 is not for, instead there is (but not fw compatible)

immagine
immagine813×398 20 KB

quectel_lc26glc26g-tlc76glc86g_series_agnss_application_note_v1-1.pdf (800.8 KB)
Quectel_LC26G&LC26G-T&LC76G&LC86G_Series_GNSS_Protocol_Specification_V1.4.pdf (956.4 KB)
quectel_lc76g_series_hardware_design_v1-3.pdf (1.3 MB)
P.s ask for a new fw in another post explicitly and give your $PQTMVERNO*58
Regards

3

thank you for your response <
is it possible for a warm start with out the backup power and with the EASY

4

Think no,but ask it also in the post for new fw…

5

Beware, from what I’ve seen, Vbkp should be powered at all time, and not just Vcc. It powers memory and some core features you need.