In several cases it might be required to provide Amélie with setup or status information, or to have Amélie provide a sort of running commentary on her status.

The problem is, a basic 16-key keypad requires eight I/O lines to decode (4x4), and an LCD has its own I/O requirements which range from 6 lines to 10 or more.

It was considered that a better alternative would be to provide Amélie with a 2400bps serial link. For the cost of only one more IC (plus a few parts), the keyboard and display (which could include real-time graph plotting and/or logging) could be pushed onto a computer (the one you're using now will be fine, thank you!)... or at least, a "dumb terminal".

Page Three (&0200-&02FF ) is reserved for the serial buffering. It is split into 128 bytes input, 96 bytes output, and 32 bytes for status and internal pointers. The reception of serial data takes place under interrupt, and upon reception a vector is called so the data in the buffer can be serviced.
 

The serial interface presented to the external world will be a standard 9-pin D so any decent null-modem cable will allow interfacing. It is likely that Amélie's BIOS will 'sample' DTR to know whether or not a cable (and responsive computer) is connected.