Measurement Computing USB-3102 - Manual (Page 17)

USB-3102 User's Guide Functional Details
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Digital I/O terminals (DIO0 to DIO7)
You can connect up to eight digital I/O lines to the screw terminals labeled DIO0 to DIO7 (pins 21 through 28).
You can configure each digital bit for either input or output.
When you configure the digital bits for input, you can use the digital I/O terminals to detect the state of any
TTL level input. Refer to the switch shown in Figure 8 and the schematic shown in Figure 9. When the switch is
set to the +5 V USER input, DIO7 reads TRUE (1). If you move the switch to DGND, DIO7 reads FALSE (0).
Pin 53
DGND
Pin 56
+5V Pin 28
DIO7
Figure 8. DIO7 detecting the state of a switch
+5V DGND
DIO7
Figure 9. Schematic showing DIO7 detecting the state of
a switch
For more information on digital signal connections
For more information on digital signal connections and digital I/O techniques, refer to the Guide to Signal
Connections (available on our web site at
www.mccdaq.com/signals/signals.pdf ).
Digital I/O control terminal (DIO CTL) for pull-up/down configuration
All digital pins are floating by default. When inputs are floating, the state of unwired inputs are undefined (they
may read high or low). You can configure the inputs to read a high or low value when they aren’t wired. Use the
DIO CTL connection (pin 54) to configure the digital pins for pull-up (inputs read high when unwired) or pull-
down (inputs read low when unwired).
 To pull up the digital pins to +5V, wire the
DIO CTL terminal pin to the +5V terminal pin (pin 56).
 To pull down the digital pins to ground (0 volts), wire the
DIO CTL terminal pin to a DGND terminal pin
(pin 50, 53, or 55).
Ground terminals (AGND, DGND)
Eight analog ground ( AGND ) connections provide a common ground for all analog voltage and current output
channels. Three digital ground ( DGND ) connections provide a common ground for the DIO , CTR , SYNCLD and
+5V connections.