TRANSISTORS ARE USED IN DIGITAL SYSTEMS AS ELECTRONIC SWITCHES. THESE SWITCHES ARE CALLED LOGIC GATES. A SINGLE TRANSISTOR CAN ACT AS ONE LOGIC GATE. A VARIETY OF THESE SWITCHES CAN BE ARRANGED TO FORM A BLOCK. A LARGE NUMBER OF SUCH BLOCKS ARE USED IN AN INTEGERATED CIRCUIT. ALL POSSIBLE COMBINATIONS OF INPUTS AND OUTPUTS BY A LOGIC GATE OR BLOCKS OF GATES CAN BE TABULATED. SUCH A TABLE OF VALUES IS CALLED A TRUTH TABLE. THERE ARE BASICALLY FIVE TYPES OF LOGIC GATES. FROM THESE, MORE COMPLECATED BLOCKS OF GATES CAN BE CONSTRUCTED. THE TYPES ARE AS : NOT, AND, OR, NOR & NAND. THERE IS ALSO ANOTHER TYPE WHICH IS KNOWN AS EXCLUSIVE - OR. IN THE TRUTH TABLES ZERO REPRESENTS FALSE & ONE REPRESENTS TRUE.
WHAT EVER WILL BE THE INPUT, THIS GATE WILL REVERSE ITS OUTPUT. IT CAN BE SEEN IN THE TRUTH TABLE ON THE RIGHT SIDE OF THE DIAGRAM, THAT FOR INPUT 'B', THE OUTPUT 'C' IS REVERSE.
IN THE 'AND' GATE THERE ARE TWO INPUTS, IN THIS CASE 'A' & 'B'. THE OUPUT 'C' WILL ONLY BE TRUE WHEN BOTH THE INPUTS ARE TRUE, IF EVEN A SINGLE ONE IS DIFFERENT THE OUTPUT WILL BE DIFFERENT. THIS CAN BE SEEN IN THE TRUTH TABLE.
THE OR GATE IS DIFFERENT THAN THE AND GATE BECAUSE IT NEEDS ONLY ONE INPUT TO BE TRUE, IN ORDER TO GIVE A TRUE OUTPUT. THIS CAN CLEARLY BE SEEN IN THE TRUTH TABLE ON THE RIGHT SIDE OF THE DIAGRAM.
THE NOR GATE IS THE COMBINATION OF TWO GATES, OR AND NOT. THE NOT GATE IS ATTACHED TO THE OR GATE WHICH CAN BEEN SEEN AT THE TIP OF THE OR GATE. HOW THIS GATE WORKS IS THAT THE OUTPUT FROM THE OR GATE IS REVERSED BY THE NOT GATE. E.G. IF THE TWO INPUTS FOR 'A' & 'B' ARE 0 & 1 REPECTIVELY THEN THE OUTPUT HAS TO BE 1, BUT THE NOT GATE AND THE END REVERSES IT TO 0.
THIS GATE HAS THE SAME THEORY BEHIND IT AS THE NOR GATE BUT IS BASED ON THE AND GATE. E.G. THE TWO INPUTS ARE 1 & 0 THEN THE OUTPUT SHOULD BE 0 BUT THE NOT GATE AT THE TIP REVERSES IT TO 1.
THIS IS AN OR GATE WITH ONLY TWO INPUTS. THE RESULT OF THE INPUTS IS ONLY TRUE WHEN BOTH THE INPUTS ARE DIFFERENT FROM EACH OTHER. WHEN THEY ARE SAME THEN THE OUTPUT WILL BE FALSE.
