How does the Entrex/Nixdorf "Trapezoid" Data/Terminal work?

Well, we don't know yet...but we're working on it.  For starters, here's some context to see how it was advertised:

Datamation - April, 1977 - Pages 56-57

Computerworld - June 13, 1977 - Page 52

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MiniMicro Systems - June, 1976 - Front Cover & Page 3

Click here for HIGH resolution image

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Backplane Connections - Entrex/Nixdorf Trapezoid

Hacking the EPROM(s)