Difference between slave ports and auxilliary I/O bus?

The slave port is a parallel communication port that can be used to communicate with an
external master device. The slave port consists of three data input and data output registers,
and a status register.

The Rabbit 4000 can enable a separate auxiliary I/O bus for external devices to keep bus
loading on the memory bus at an acceptable level. This bus consists of eight data lines on
Parallel Port A and up to eight address lines on Parallel Port B. This functionality is mutually
exclusive with the slave port and regular parallel I/O on Parallel Ports A and B.
When enabled, the address lines of the auxiliary I/O bus hold their value until a new value
is written to them. The data lines return to a tristate mode after each transaction.