[gta02-core] Modem schematic / RF help needed

[Werner Almesberger]

Rask Ingemann Lambertsen wrote:
>    I was thinking of just connecting the switch in parallel with R8101
> (currently 0R that we would make NC) and connecting the enable input
> (ON/OFF) to the GSM_2V8 supply.

Oh, that would be a very elegant solution. Since the level shifter
is operating only in the CPU -> modem direction, there should be
no risk of the modem accidently keeping GSM_2V8 up.

> requirements of the GE865. Right now I'm also confused by the lack of a
> connection from the GSM_2V8 supply to the modem. Does it have an internal
> 2.8 V LDO to derive the I/O voltage from the 3.8 V supply?

Yup. It's rather strange that they don't export a few mA of that
juice for level shifters.

- Werner