8.5  Serial Communications 

A graphical representation of the Gemini Serial socket is pictured left (i.e. Pin D is 

closest to the top of the Gemini main Panel)  

Either a DB9 or DB25 connector can be used for serial communications to a PC.  

9 

 25 

Pin

pin

Name

In/Out

Connected to

1

8

DCD

In

NC (or bridged to RTS)*

2

3

RD

In

Gemini A

3

2

TD

Out

Gemini B

4

20

DTR

Out

bridged to DSR*

5

7

GND

Gemini C

6

6

DSR

In

bridged to DTR*

7

4

RTS

Out

bridged to CTS (and 

DCD)*

8

5

CTS

In

bridged to RTS*

9

22

RI

In

NC*

NC= Not connected

* = Optional connection, e.g. serial pins 2,3 & 5 are often all that are required to be 

connected on a 9 pin port.

Gemini Users Manual 

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