Author Topic: Shall I supply power to the VBACKUP pin?  (Read 7562 times)


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Shall I supply power to the VBACKUP pin?
« on: June 07, 2010, 06:00:57 PM »
Q: Shall I supply power to the VBACKUP pin?

VBACKUP (formerly: BACKUP_PWR) should be connected in all cases. It draws a small amount of current to refresh the Volatile Memory (VM) in the GPS module.

If it is not connected, the module will always perform a cold start once it is powered on because the navigation data and time stored in the VM will be lost, and this will result in longer TTFF (which is also dependent on GPS signal reception quality). In addition, because the parameter settings (set by the MiniGPS tool or through command, such as changing baud rate from 9600 to 38400) are also stored in the VM, these configurations will be lost and be reverted back to the default firmware value if VBACKUP is not connected (in the previous example: baud rate back to 9600).

If VBACKUP is connected and the previous data stored in the VM are valid, the TTFF time will be drastically reduced (hot-start or warm-start, depending on the length of time between each power-on).

Things like RTC almanac/ephemeris and last known position as well as some other proprietary data are stored inside the VM.

Typically you should see the GPS module perform a hot start if it is powered on within 2 hours of being turned off. (assuming VBACKUP is connected, of course).

The GPS module will perform warm-start if it is powered on after more than 2 hours.

If the ephemeris/almanac is determined to be unusable by the MediaTek calculations, such as when the receiver is moved across great distances or the ephemeris /almanac simply expires, then the receiver will perform cold-start. Typically you will see the module perform cold start if it has been off for several days.
« Last Edit: June 10, 2010, 04:49:01 PM by Horsa »