On Fri, 14 Apr 2017, Peter Cetinski via cctalk wrote:
The EI expansion port was originally called the Screen Printer port
because that was the only accessory that connected directly to the
TRS-80 bus.
Originally.
Later, the Voice Output device (repackaged Votrax?) used the bus
connector.
Later, the Voice Input device used the bus connector.
After we (Elcompco) built a 4 port "Bus Extender" (with active
termination), we found that the Voice Input device had a hidden
undocumented pass-through of the bus. All essential to connecting an X-10
interface and being able to say, "LET THERE BE LIGHT!", with a response of
X-10 "all lights ON", and a voice responce of "BY YOUR COMMAND". Thus
demonstrating the level of practical applicability of a home computer.
