L76K cold and hot start for low-power periodic location acquisition

IoT Modules GNSS Module
1

Dear Support,

I am currently evaluating L76K GPS module.

First of all, I haven’t found any Quectel doc targeting L76K specifically. Is GNSS L76 | Quectel link correct for documents applicable to L76K module?

Provided the above is true, the Lx6&LC86L&LG77L Series GNSS Protocol Specification document specifies following vendor-specific commands:

  • PMTK101 PMTK_CMD_HOT_START
  • PMTK102 PMTK_CMD_WARM_START
  • PMTK103 PMTK_CMD_COLD_START
  • PMTK104 PMTK_CMD_FULL_COLD_START
  • PMTK161 PMTK_CMD_STANDBY_MODE

Application logic I am planning to use for the product I am working on is based on following scenario:
(1) put the L76K into low-power state by switching-off VCC supply via transistor (while keeping V_BCKP powered)
(2) wake-up the L76K after application-specific time period (i.e. 24 hours) by switching-on VCC supply
(3) wait for GPS fix
(4) save the GPS location on microcontroller driving L76K
(5) start-over with step (1)

I have following questions regarding the steps above:

  1. is this scenario aligned with Quectel recommendations for low-lower L76K GPS periodic location acquisition?
  2. should be L76K put into STANDBY_MODE before step (1) or it does not matter?
  3. Doc for PMTK_CMD_HOT_START mentions that:

“Normally a hot start means the GNSS modules are powered down less than 2 hours with RTC in operation and the ephemeris is still valid. As there is no need for downloading ephemeris, it is the fastest startup method”

Does it mean PMTK_CMD_COLD_START shall be manually triggered on L76K after step (2) when more than 2 hours elapsed since last GPS fix?

  1. Does PMTK_CMD_*_START matter after VCC is switched-off and switched-on in steps (1) & (2) given the V_BCKP is always powered? Or switching VCC off and on forces the cold start on L76K despite backup data?

I am looking forward for answers for the questions above to properly utilize L76K in the product I am working on.

Best regads,
Nikodem

2

Dear Tech Support,

I have experimented a bit myself and it turned out L76K supports only PCAS messages, while PMTK messages are not supported. I think it is confirmed in this post: Firmware/Protocol version for the L76K - #2 by george.gao
Then, instead of individual PMTK_CMD_*_START commands, PCAS10 with appropriate parameter can be used.

Despite L76K not supporting PMTK messages, most of the concerns from the post above still hold:

  1. is this scenario aligned with Quectel recommendations for low-lower L76K GPS periodic location acquisition?
    2a. There is no equivalent of PMTK_CMD_STANDBY_MODE in PCAS messages. Does it mean the only way to enter low power state is to switch off VCC supply?
    3a. Should be PCAS10 with flag 2 = Cold Start issued when more than 2 hours elapsed since last GPS fix?
    4a. Does switching VCC off and on forces the cold start on L76K despite backup voltage being always applied?

Would you kindly take a look?

Best regards,
Nikodem

3

Dear,Nikodem,

This message is about report by you in 8.1.
I will send you the relevant reference documents for L76K via the email.
Regarding your question 1. This is correct. You can refer to the hardware design manual for details.
Regarding your question 2. No need.
Regarding your question 3. The L76K does not support the PMTK command.
Regarding your question reported in August 5. You can lower the standby pin to enter the standby mode, disconnect the VCC power supply for at least 1 second and keep V_BCKP powered normally.
Please refer to the hardware design manual for details.

Best regards,
Jasper