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For the purpose of explanation, a circuit representing the inputs and outputs is shown here.
Figure 39
Typical Internal Circuitry
The I/O (typical of all signal pins) has an input buffer and output driver associated with it. This
is done to provide a highly flexible hardware implementation. This parallel port is used for
implementation of the T-16 numeric display and thumbwheels. Since each of the signal pins can
be firmware configured, different features can be achieved.
Each of the I/O pins has a pull up resistor (R1) associated with it. This pull up resistor is
connected to the 37 pin connector pin 33 (+BUS). This pin can be connected to pin 25 (+5) for a
+5 volt interface. It can be connected to pin 34 (+15) for a +15 volt interface or it can be
connected to the positive source of the external device which is the preferred method. The
ground connection (29, 30, 31, 32) must be connected to the ground supply of the external
device. The shield (37) is provided as an alternative place to connect the cable shield if a
connecting place cannot be found at the external device. Never connect the shield at both ends.
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