NEC PC-8300, controlling the "8201" emulation mode
If you have an NEC PC-8300 with its original System ROM, it actually is a 128K masked PROM that has four 32K images embedded. The extra images can be switched in and out via I/O port 163 on your 8300. The computer does this behind the scenes already when you switch into TEXT or TELCOM in order to access different features of those enhanced internal programs. What NEC also did was dedicate one of the 32K ROM images for the original PC-8201A ROM. This was to provide complete backward compatibility with all existing software.
From BASIC, you can issue these commands:
Also, simply hitting the RESET button on the back of your NEC also will throw you back into the regular 8300 default mode.
- OUT 163,2: Flips your 8300 into "8201" emulation mode.
- OUT 163,0: Flips you to back to the 8300 default ROM image.