Just for fun, I wanted to see if you could run Applesoft Basic from an external terminal. So I modified the rs232 terminal to strip out the high bit with "data &= 0x7f;"

./mame apple2p -sl3 ssc -sl3:ssc:rs232 terminal

and after hitting RESET after booting, and typing IN#3 and PR#3 you can type with the terminal keyboard and send output to the terminal.

Output is simultaneous to the screen and the terminal, and the keyboards work simultaneously as well.

One thing that's interesting is that CTRL+C from the terminal will only be processed if there is an INPUT statement, so you can't break basic programs that are running.

[Linked Image from i.imgur.com]
[Linked Image from i.imgur.com]

Micro Display Systems made a full page display called the "Genius Full Page Display Model 101" that had 57 lines * 80 column resolution with RS232 and Apple specific versions. That would have been pretty neat. I think that once 80 columns was ubiquitous with the //e that demand for external terminals faded along with the additional complexity and high cost.