I'm designing a small development board (from schematic design to PCB), centered around an ATmega32U4 MCU, and a Quectel M95 GSM module. I'm using the M95 Hardware Design Manual (http://www.quectel.com/UploadImage/Downlad/M95_Hardware_Design_V1.3.pdf) and there's a part that I don't understand for the UART reference design, to connect the M95 to the ATmega32U4 MCU.
I don't particularly understand which reference design to go with? The first one makes sense, you just connect the UART pins from the MCU to the GSM module. The second one also makes sense: if your MCU is based on 3.3V (which mine is), then this is the reference design to follow in order to have a voltage drop of 2.8V, in order to satisfy the DC characteristics listed above (?). I'm unsure which one to go with? Does it matter?