Logic is what we make of it, it's as simple as this.
 Each logic gate type "AND, OR, NAND, etc..." has defined rules which are called truth tables. As long as you follow these rules everything will be logical and work out correctly.
 
Normally zero "0" is a logic low like ground and one "1" is a logic high like positive five volts.

xyz01.jpeg
A and B are inputs.
X is the output result.
Yet if helps you to relabel them feel free as long as you keep the same rules.
  Like an XOR for example, with two thumbs down we get a frown :(, with only one thumb up  "either one" we get a smile :), with two thumbs up we get that frown back :(.

 With the all OR gates circuit, following it's truth table we get a high out if any, or all, of the sixteen inputs go high. This would work well for an alarm circuit monitoring change.

Now lets see if you have the logical mind to complete the following: 8to3-encoder.html
Logic gate truth tables.                All OR gates circuit.
gates.gifOR.png


  It's a long way to go from a switch on the test board to parallel port, processed, parallel port back to test board and have a LED turn on.
Just having hardware switch which people touch and the LED feedback makes the learning more fun for me and hopefully others.
 
 Use input pin 15 of lpt0, lpt1 for logic in A & B and pin 17 of lpt2 for X in the following:
#Written scripts for SI/OP to emulate standard logic gates via ports input(s) and output.
#AND_gate.sh
#!/bin/bash
while true ; do
VALUE_A=`cat /home/siop/port0/pin15`
VALUE_B=`cat /home/siop/port1/pin15`
VALUE_X=2
  if [ $((VALUE_A+VALUE_B)) = $VALUE_X ] ; then
    echo "1" > /home/siop/port2/pin17
  else
    echo "0" > /home/siop/port2/pin17
  fi
sleep .5
done

 #NAND_gate.sh
#!/bin/bash
while true ; do
VALUE_A=`cat /home/siop/port0/pin15`
VALUE_B=`cat /home/siop/port1/pin15`
VALUE_X=2
  if [ $((VALUE_A+VALUE_B)) = $VALUE_X ] ; then
    echo "0" > /home/siop/port2/pin17
  else
    echo "1" > /home/siop/port2/pin17
  fi
sleep .5
done
#OR_gate.sh
#!/bin/bash
while true ; do
VALUE_A=`cat /home/siop/port0/pin15`
VALUE_B=`cat /home/siop/port1/pin15`
VALUE_X=0
  if [ $((VALUE_A+VALUE_B)) = $VALUE_X] ; then
    echo "0" > /home/siop/port2/pin17
  else
    echo "1" > /home/siop/port2/pin17
  fi
sleep .5
done

 #NOR_gate.sh
#!/bin/bash
while true ; do
VALUE_A=`cat /home/siop/port0/pin15`
VALUE_B=`cat /home/siop/port1/pin15`
VALUE_X=0
  if [ $((VALUE_A+VALUE_B)) = $VALUE_X ] ; then
    echo "1" > /home/siop/port2/pin17
  else
    echo "0" > /home/siop/port2/pin17
  fi
sleep .5
done
#XOR_gate.sh
#!/bin/bash
while true ; do
VALUE_A=`cat /home/siop/port0/pin15`
VALUE_B=`cat /home/siop/port1/pin15`
VALUE_X=1
  if [ $((VALUE_A+VALUE_B)) = $VALUE_X ] ; then
    echo "1" > /home/siop/port2/pin17
  else
    echo "0" > /home/siop/port2/pin17
  fi
sleep .5
done

 #Inverter
#!/bin/bash
while true ; do
VALUE_A=`cat /home/siop/port0/pin15`
VALUE_X=0
  if [ $VALUE_A = $VALUE_X ] ; then
    echo "1" > /home/siop/port2/pin17
  else
    echo "0" > /home/siop/port2/pin17
  fi
sleep .5
done