Figure 2-23. Logic gate combinations: A. Simple combination of AND gates; B. Simple combination of AND gates and
The output Boolean expression of gate 1 is RS, and the output expression of gate 2 is TV. These two
output expressions become the inputs to gate 3. Remember, the output Boolean expression is the result of
the inputs, in this case (RS)(TV); spoken "quantity R AND S AND quantity T AND V."
In view B we have changed gate 3 to an OR gate. The outputs of gates 1 and 2 remain the same but
the output of gate 3 changes as you would expect. The output of gate 3 is now (RS)+(TV); spoken
"quantity R AND S OR quantity T AND V."
In figure 2-24 (view A), the outputs of two OR gates are being applied as the input to third OR gate.
The output for gate 1 is R+S, and the output for gate 2 is T+V. With these inputs, the output expression of
gate 3 is (R+S)+(T+V).