External Expansion

According to section "20.3 External Device Expansion Function Timing" in Chapter 20 EXTERNAL DEVICE EXPANDED FUNCTIONS in the uPD78F0034 User's Manual, control signals other than RD and WR are output even during periods other than external access; but in the case of a device activated just with the CS signal, the select signal indicating the external access time must be supplied.
Is there a method other than full decoding of A0 to A15 externally?

It is not possible to control an external device only with address decoded signals.
All the bits of the address are not switched without time delay when an address signal is switched to; some time is needed for switching, and during this time, an address signal other than the normal address is output.
When control is performed only by address decoding, an abnormal control signal may be output.
In order to prevent this, it is necessary to use an address with RD or WR.

What is the method for accessing the external device that is mapped at addresses F000 to F005 as the input port and F010 to F015 as the output port when using the external device expansion function?

The method involves defining the variables in C language.
Use the following declaration format.

    #pragma section @@DATA EXTDATA1  AT 0F000H
     unsigned char  indata0;            /* Input definition */
     unsigned char  indata1;
          :
     unsigned char  indata5;
    #pragma section @@DATA EXTDATA2  AT 0F010H
     unsigned char  outdata0;           /* Output definition */
     unsigned char  outdata1;
          :
     unsigned char  outdata5;
    #pragma section @@DATA @@DATA

After defining the above, create a link directive file and then define the memory area from F000 as shown below.
Here, define F000 to F0FF as EXTRAM.

      MEMORY  EXTRAM : (0F000H,100H)

These processing actions make it possible to read external data by referencing indata0 to indata5.
Similarly, data written to outdata0 to outdata5 is output.