This was one of those cards that I used to dream of owning but could never justify! There are two Zilog SIO ICs with two serial ports on each. These are/were a very sophisticated device at the time, being fully programmable to produce almost any bit rate and combination of start, stop and parity bits that could be imagined. The card also has its own clock generator crystal so that the resulting bit rates remain accurate no matter what the user has done to the system clock!In addition, Gemini “threw in” another old favourite, the Zilog PIO, with all its I/O pins connected to a header for connection by a ribbon cable.
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