SIM900A shield

[Karthik rajagopal]

Hi all,
I started working with my project which requires the use of SIM900A. My code gets executed with arduino and GSM without any problem. But I will be using a 3.3V microcontroller whose I/O pins are not 5v tolerant. I am using a SIM900A GSM shield from Astar. I did some continuity test on the board to find out two MOSFETs connected to the Rx and the Tx pins in the configuration I have shown below(the same was for Rx also).


I thought this could be a level shifter but none of the circuits for a level shifter that I found on internet matched with this...all had their souce and gate connected. Will it be safe to connect my GSM directly to the MCU?
I also tried connecting the Tx pin of the GSM to the MCU through a voltage divider,but it did not work.
Please help.
Thanks in advance.

 

[Harald Kapp]

two MOSFETs connected to the Rx and the Tx pins in the configuration I have shown below

Are you really certain you didn't mix up source and drain when extracting the hand drawn circuit?

It looks like this module has a RS-232 interface, not TTL, on the D-SUB connector.

 

[Karthik rajagopal]

Are you really certain you didn't mix up source and drain when extracting the hand drawn circuit?

It looks like this module has a RS-232 interface, not TTL, on the D-SUB connector.

Thanks for the reply.
Even I was confused with that..I checked it several times ,don't know why they have connected it that way . I have attached the part no. along with its image. The GSM board also has TTL ports...