GTCO Super L III - Users Guide - Manual (Page 38)

Super L III 38
Data Terminal Equipment (DTE), such as printers, digitizers and computers, usually (but not
always) transmit data on Pin 2 and receive data on Pin 3. Data Communications Equipment
(DCE), such as modems, generally transmits data on Pin 3 and receives data on Pin 2. Thus,
connecting a terminal (DTE) to a modem (DCE) may be as simple as connecting them with a
straight-through cable that is wired pin-to-pin (i.e., 1 to 1, 2 to 2, etc.). The figure below
shows such a cable. The Super L III Controller is typically connected in this manner using
the cable supplied by GTCO CalComp by Turning Technologies.
Connecting DTE to DTE or DCE to DCE may require a different strategy to get the data on
the correct wires. The figure below shows a cable that can work in this situation. It is called
a null modem cable and it fools both devices into thinking they are talking with the right
kind of receiver. This cable routes Pin 2 to Pin 3 and Pin 3 to Pin 2.