I'm trying to put together a voice recorder/playback system using an SD card and a bought in FAT16/FAT32 driver from Embedded.com. I am using the SPI interface. I am finding that different cards behave differently under similar conditions, with most of them failing the initialise phase. I am getting responses from the card indicating illegal commands but I can see data in the correct places. Other times I get a response from the card which has been clocked out at the wrong time (e.g 2 clock pulses late). This all seems to point to clocking problems but I am running at about 1MHz after the initial 400kHz stage. I have turned on/off the slew rate limiting. I have tried using the high drive capability on the SPI pins, and combinations of both. Has anyone had any similar problems. At present I have a hand wired board but with very short ( < 1cm) wires to the SD card. I have a pcb on it's way but am running out of ideasif that doesn't sort it.