Voltage levels

Newbie · Guest

Hi,

I want to run a 18F252 at 3.5v along with a GM862 GSM modem but I think there is an issue with level conversion as the GM862 has a maximum 2.8v for the interface can anyone advise me? do I mmet conversion?

Thx

Pete

Newbie · Guest

Hi again,
I notice losts of people looking at my post but nobody answering, am I asking the wrong question or is it that simple you think I'm stupid?

I'm just unsure if I need voltage level shifters for the RS232 and I/O control to this device (max 2.8v) whilst running a PIC at 3.5v

Anyone?

Steve Lomas · Guest

The 18F252 has a 4.2V minimum so will not run at 3.5V.
The 18LF252 will do as you require but with limitations on the max clock frequency.
I'm just developing a module with an 18F252 & GM862, I'm running the PIC at 5V and the GM862 from a LiIon battery. To acheive the level shifting I have used the BCR22 devices as per the Telit documentation.

Hope this helps.

Guest · Guest

OK, so if I used the 18LF252 at say 3v and at 4mhz would I need level shifters for the RS232 link to the GM862?

Thanks

P.S. Sorry to be such a newb

Haplo · Joined: 06 Sep 2003 Posts: 659 Location: Sydney, Australia

In the GM862 datasheet section 7.1 "Using GPIO as input" it explains how to perform the necessary level conversion.

Ttelmah · Guest

For a similar application in the past, I used the MAX3372.

Best Wishes

Newbie · Guest

So although you didn't say it, I assume from the last couple of replies that even if I run the 18LF252 at 3v I still need to level [censored] to work with the GM862 at 2.8v?

Thanks

Newbie · Guest

I mean shifters!!!!!

Ttelmah · Guest