M [start_address] [end_address]

* M is a memory contents dumping command.
* Typing M with a start and end address will display the hex and
  ASCII contents of those bytes in the memory locations specified.
* Typing M with only a start address will display 160 bytes
  starting at the location specified.
* Typing M with no parameters will display 160 bytes starting
  from the current memory location.
* The current memory location is always one location higher than
  the last location shown by a prior M command.

eg.   m $70000 $77fff
      m $fc0000
      m