Thanks dabi
But actually I am developing my proyect. I have seen a lot of proyects but none of them have been of great help.
The thing is that you need to send some clock cycles to the slave device, and when generating the clock cycles I think that the device might take them as a zero comand, and that would be returning to the begining, the reset sequence. On the other hand, the AVR 8535 stops sending clock cycles after the transmission of a single byte, so I have to do some sutff in order to send the clock cycles, wich leads us to the point that the MMC will take it as a zero comand.
Any ideas?