Why MCU(pic16f877A) don't recieve data from SIM300CZ

[tannhatrang]

I have a project use 1 SIM300CZ connect PIC 16F877A but PIC don't receive data from SIM300CZ.

I did example to test this case:
Ex 1: - I do connect SIM300CZ with Computer(Hyper Terminal) via MAX232, This case it send and recieve data between SIM300CZ and Computer very good.

Ex 2: I do connect PIC with computer via MAX232, this case, it send anh recieve data between PIC and computer very good.

But: When connect PIC with sim300cz don't use MAX232 , connect direct , PIC send data to SIM300C is OK. but SIM300CZ send data to PIC is not OK.

I use baudrate: 9600,n,8,1
Why?
Help me.

 

[nandhu015]

Both are fine. Check tx and rx while connecting gsm and microcontroller. You have to swap tx and rx.(Null modem connection)

 

[tannhatrang]

Hello!
I do suscessfull for this project . I search a error is: I miss supply 5v for Transistor to change voltage from PIN TX of SIM300cz to MCU.

Bye