I am working on drawing a PCB for an SMS system with Quectel M10 module. I want to have a single power supply of 4V and would like to run the whole system with it. I am reading the datasheet and following the hardware instructions as given there (http://www.auroramobile.ru/content/f...0_hd_v1.01.pdf). My power supply will be able to provide 2.5Amp output.

I know sometimes some datasheets do not give you the full information or sometimes miss some important resistor or capacitor. So I would like to ask here if someone has tried this before, doesn't have to be with the same module and added something extra which is needed. As I will be connecting the UART pins of my 16F877A to the modem's Tx/Rx directly, I would also like to ask if I should connect them directly of put some resistance in between, if yes, then what value and should I hold any one of them high/Low etc.

My plan is to just connect the SIM CARD holder using 4 lines only, Vdd/Data/Clk/Rst with 22Ohm resistance in between except in VDD connection. and use the Tx/Rx lines with my PIC. I also want to leave the arrangement for DTMF decoder IC, so I wanted to ask which output is suitable for the input of this IC, single ended SPKer output or differential type output.

If someone has attempted is before, please share your experience here so me and others can learn from it. Thanks