Do you know what is the maximum time in writing process between CMD sending and data. In specification is diagram: where P means one-cycle pull-up and * means repetition. So I understand it that after write command card waits for data start bit (S). But it doesn't work for me if I send data from PC. In this scenario I send CMD and then I wait for 512 data bytes and then if available I start sending them on data lines. But I can write data if I try with some constant values saved in code. So then I don't have to wait and I start writing couple of cycles after CMD.