Hy again ! 
Thanks for your help !
With your advice i do a lot of progress, but I have some problems again.
I have two serial interface with my programm.
My grove gps are a u-blox version, is baudrate are 4800-57600.
With the oscilloscope I measure the baudrate and it's exclatly 4800.
The oscilloscope see data's but it's imposible to see this data's in the port COM of arduino.
The Tx(GPS) wire is connected to the Rx pin(Arduino Mega) in 8.
But it doesn't work. I have this message...
"DIAGS Chars=0 Sentences-with-Fix=0 Failed-checksum=0 Passed-checksum=0
WARNING: No GPS data. Check wiring."
Thanks in advance Hugo
