The main I/O used by micro controllers are the parallel ports , the 68HC11F1 has seven  8 bit ports namely Port A,B,C,D,E,F and G . The use of ports depends on the mode configuration of the system and the use of the other peripheral devices, since they share pins. In order to program the ports we need to write/read data to special registers, the area from 0x1000 to 0x105f is memory mapped to the peripheral devices.  NOTE: The monitor has moved the register block to start at 0x00 i.e Padr = 0x00, Paddr = 0x1 etc.

Below are shown the RAM based I/O registers i.e. 0x0 to 0x0a
 
  Address   Register
 
  0x0000  Port A register Padr
   0x0001  Port A Data direction register Paddr
  0x0002  Port G register Pgdr
  0x0003  Port G Data direction register Pgddr
  0x0004  Port B register Pbdr
  0x0005  Port F register Pfdr
  0x0006  Port C register Pcdr
  0x0007  Port C Data direction register Pcddr
  0x0008  Port D register Pddr
  0x0009  Port D Data direction register Pdddr
  0x000a  Port E register Pedr
 
Port A, D, are bi-directional 8 bit ports and have alternate uses G timer, serial comms and chip selects respectively.
 
Port B is an 8 bit general purpose output port with alternate function as the upper address bus in the extended mode.
 
Port C is a general purpose 8 bit port with alternate functions as the data bus in the extended mode
 
Port E is an 8 bit general purpose 8 bit input port with an alternate function as the ADC input
 
Port F is a 8 bit general purpose output port with alternate function as the lower address bus in the extended mode.
 
On the target system provided the 68HC11 is set in extended mode therefore the only ports available are A,D,E and G since B,F form the address bus and C forms the data bus to the EPROM. Each register is bit defined in that each bit configures one feature of the respective port , however all the data registers and data direction registers work on the same principle.