Model 301
24-bit USB Data
Acquisition System
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OPERATION
Digital Input/Output


The digital input word, from pins 5 through 12 on the input/output connector, is updated with each conversion in polled mode and with each packet of ten conversions in normal scanning mode. For digital input scanning, the digital input byte is updated and transmitted once per conversion. The digital inputs are active low. They can be activated by a contact closure to digital ground or by any 5 volt logic signal referenced to the same ground.The digital input word is displayed as an integer between 0 and 255. You may want to view it in binary format so that individual inputs show as ones and zeros.

The digital output command puts a latched 8-bit digital word at pins 18 through 25 on the input/output connector. Valid values are in the range of 0 to 255. The digital outputs are buffered to source or sink 20mA. Note that when sinking current, the voltage may rise significantly above 0 volts.


25-PIN CONNECTOR PINOUT
  PIN 13 Digital Ground    
      PIN 25 Digital Out 7
  PIN 12 Digital In 0    
      PIN 24 Digital Out 6
  PIN 11 Digital In 1    
      PIN 23 Digital Out 5
  PIN 10 Digital In 2    
      PIN 22 Digital Out 4
PIN 9 Digital In 3    
      PIN 21 Digital Out 3
  PIN 8 Digital In 4    
      PIN 20 Digital Out 2
  PIN 7 Digital In 5    
      PIN 19 Digital Out 1
  PIN 6 Digital In 6    
      PIN 18 Digital Out 0
  PIN 5 Digital In 7    
      PIN 17 Digital Ground
  PIN 4 Digital Ground    
      PIN 16 Analog Ground
  PIN 3 Analog Ground    
      PIN 15 CHANNEL 1+
  PIN 2 CHANNEL 1-    
      PIN 14 CHANNEL 0+
  PIN 1 CHANNEL 0-    

Note: For maximum protection, any unused input terminals should be connected to ground. This is done to protect the circuitry from static discharges which can be of extremely high voltage. Open inputs can also pick up noise. Strain-relief is recommended for all permanent wiring on the connector. Otherwise, physical stress may cause the failure of an electrical connection. The connector hood provided has a strain-relief clamp.

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