3. multiplexer
- 1. MULTIPLEXER Dr. N. Anuradha Asst. Professor of Physics Bon Secours College for Women Thanjavur
- 2. MULTIPLEXER Multiplexer means many into one Many inputs, only one outputs Control signals steer any input to the output Also called data selector General idea & general circuit n – input signals m – control signals 1- output signals m control signals select 2m input signals = n < 2m
- 3. 4 - to - 1 Multiplexer Depending on control inputs A & B = one of the four inputs D0 to D3 steered to output Y SOP Operation Y = A B D0 + ABD1 + ABD2 + ABD3 If A = 0, B = 0 Y = 0 0 D0 + 0 0 D1 + 0 0 D2 + 0 0 D3 Y = 1 1 D0 + 1 0 D1 + 0 1 D2 + 0 0 D3 Y = D0 A = 0, B = 0 == upper AND gate is active, others inactive Y = D0 A = 0, B = 1 == Second AND gate is active, others inactive Y = D1 A = 1, B = 0 == Third AND gate is active, others inactive Y = D2 A = 1, B = 1 == Fourth AND gate is active, others inactive ====== Y = D3
- 5. 16 - to - 1 Multiplexer Inputs = D0 to D15 When ABCD = 0000, Upper AND = active, other gates = disabled, D0 transmitted to output Y = D0 If D0 = 0, Y = 0, If D0 = 1, Y = 1 The value Y depends on D0 When ABCD = 1111, Lower AND gate is active, others inactive Y = D15 Output Y = 8 - to - 1 Multiplexer Inputs = D0 to D7, Three control inputs When ABC = 000, Y = D0 ABC = 001, Y = D1 ABC = 010, Y = D2 ……………………….. ABC = 111, Y = D7
- 7. IC 74150 16 - to - 1 TTL multiplexer, 24 pin IC Pin 1 to 8 & 16 to 23 ===== D0 to D15 Pin 11, 13, 14, 15 ======= A, B, C, D Pin 10 = output = complement of the selected data bit Pin 9 = Strobe = enables or disables the input Low strobe = enable the multiplexer ====== Y = Dn High strobe = disable the multiplexer ====== Output = high === value of ABCD doesn’t matter Two standard methods for implementing truth table 1. Sum of products 2. Product of sum 3. Third method is multiplexer solution i.e., complementing each Y output = data input
- 9. Multiplexer Logic Complementing each Y output = data input 1. D0 = î = 0 2. D1 = ô = 1 ……………. D15 = î = 0 Bubbles on Signal lines Bubble on the line = complement Bubbles = indicate active low signal Nibble Multiplexer Input = 4 bits = nibble = A3A2A1A0 = B3B2B1B0 SELECT = determine which nibble is transmitted to output SELECT = Low = Four NAND gates on left activated Y3Y2Y1Y0 = A3A2A1A0 SELECT = High = Four NAND gates on right activated Y3Y2Y1Y0 = B3B2B1B0
- 10. Nibble Multiplexer – IC 74157 Has Strobe input Strobe is active low input Strobe = low ==== multiplexer is active Strobe = high ==== multiplexer is inactive