According to document "Rabbit® 6000 Microprocessor. User’s Manual 90001108_", PortA can be all output or Input but not
Parallel Port A uses pins PA0 through PA7. These pins can be used as follows.
• General-purpose 8-bit data input (write 0x080 to SPCR)
• General-purpose 8-bit data output (write 0x084 to SPCR)
The reason is because Port A has a single direction setting for all pins.
The other ports have a data direction register (e.g., PBDDR) to set the direction of individual bits.
Sep 30, 2020