read_mbr.c

if (sd_init() == SD_OK) {
    unsigned char buf[1024];
    if (sd_readblock(0, buf, 1)) {
        for (int i = 0; i < 512; i++) {
            if (i % 16 == 0) {
                printf("%04x:", i);
            }
            printf("%02x ", buf[i]);
            if ((i + 1) % 16 == 0) {
                printf("\n\r");
            }
        }
    }
}