JLCooper eBOX GPI8 - Manual (Page 50)

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The inputs of the eBOX GPI8 GPI ports on the 25 pin D-
subminiture connector are CMOS inputs. The input circuitry has a
4700 ohm pullup resistor to +5 volts as referenced to pin 1 of the
GPI Input Port.
Note: Because the inputs are CMOS, the input voltage MUST be
limited to voltage levels between 0 and 5 volts. If this is not possible,
consider using the eBOX I/O.
The internal pullup resistor insures that the input pin is set to a
known state. The default state of the GPI Inputs is +5 volts or a
logic state of ‘1’ in the GPI message bitmap. The internal pullup
resistor also allows a simple switch or ‘dry contact’ to be
connected between a GPI Input pin and ground as shown in the
example below.
74HC244
5 Volts
Detail of GPI Input
4700Ω
4700Ω
74HC244
5 Volts
GPI Input Example with Pushbutton Switch
1
2