MiSmSDCard

plc ----------------------+
 |                        |
 | host                   |
 | socket                 |
 | debug                  |
 | read_word()            |
 | write_word()           |
 | read_bit()             |
 | write_bit()            |
 |                         \
 | SD -----------> MiSmSDCard
 |                           |
 +---------------------------+