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21:56, 10 August 2010 Here is a list of some "unknown" [[RS232]] interfaces. "Unknown" meaning that the devices are so rare that nobody did ever see them. And it isn't even confirmed that they did exist at all.
Below adverts do sound as if the companies did actually develope their "own" RS232 solutions - although it's also possible that they only redistributed [[RS232|known RS232 interfaces]] from other developers.
== Griesmayer ==
[[File:Griesmayer RS232 and Centronics Advert (CPC Schneider International, issue 12-1985, page 22).jpg]]
'''Griesmayer Electronic''' advertised "E.B.S. 464" (Expansion Board System) modules for 464/664: a '''IF1 parallel/serial data''' interface ([[RS232]], plus [[8bit Printer Port]]). As well as '''IF2 universal I/O''' interface, and '''SE1 5-slot motherboard''', and SK1/SK2 cables.
== Gundermann ==
[[File:Gundermann Dual RS232 Advert (CPC Schneider International, issue 12-1985, page 21).jpg]]
Gundermann Mikroelectronik - advertised a '''dual highspeed rs232''', and (a separate product) a '''48-pin parallel I/O''' interface.