2.8V interfacing

[tom.k.cook]

I'm trying to use the Raspberry Pi's UART (on GPIO14 and 15) to interface to a SIM5320E GSM module. The UART on the SIM5320E is 2.8V logic - logic high is at least 2.15V.

I can't find anywhere the logic level range for the GPIO pins on the Pi. Will driving them with 2.15V work?

I already need some level shifting because the SIM5320E is not 3.3V-tolerant - but shifting down is easier to sort out than shifting up.

[joan]

I think you may be hitting an unreliable marginal area with 2.15V.

http://www.mosaic-industries.com/embedd ... ifications

I haven't noticed problems with 2.5V.

[Burngate]

Not sure why shifting up is harder than shifting down.
This works both ways.

LevelShiftSch3.png (15.2 KiB) Viewed 695 times

As long as the fet threshold is low enough (for NDS331N Vgs(th) is between 0.5v and 1.0v) it should just work.