 Hello and welcome to the video lecture on bidirectional shift register. Myself Mitz Enes Naik. At the end of this session, students will be able to describe the working of bidirectional shift register and they will be able to implement N-Bit bidirectional shift register. So before moving towards the concept of bidirectional shift register, you have to recall the basics of shift registers and their basic mode of operations like CISO, CPO, PISO and PIPO. So let us see more about it. So the bidirectional shift register is a type of shift register in which the data bits can be shifted either from left to right or from right to left, bit by bit means here serial in and serial out, shift left and shift right operation is allowed. So how many number of flip-flops we can use there, we can call it as N-Bit bidirectional shift register. For example, if we use 6 flip-flops then we can call it as 6-Bit bidirectional shift register. So this is the 4-Bit bidirectional shift register block diagram. Here 4-Bit flip-flops are used and each and every flip-flop is fed with the output of OR gate. Here the input of OR gate is fed with 2 AND gate outputs. As you can see here the OR gate 1 is fed with AND gate G1 and AND gate G5. Like that there are 8 AND gates and 4 OR gates available in the specific manner. As it is synchronized circuit the common clock is given to each and every flip-flop. Now we can call it as the flip-flop D0, D1, D2 and D3 and the corresponding outputs are Q0, Q1, Q2 and Q3. Now there are two input lines given. First is serial data input which is connected to gate G1 as well as it is connected to gate G8. So we will see what is the purpose behind this in the upcoming working section. The second input line is right-left bar. Here the right-left bar is also called as mode signal. It will allow the circuit to work as either shift-left or shift-right operation. The connections are like this. The first connection is output Q0 is fed to gate G2 of the next input logic of flip-flop. Output Q1 is fed to G3 that is input logic of next flip-flop D2. Like that so on each and every output of previous flip-flop is fed to the input logic of next flip-flop. There is another connection available. The output Q3 that is the output of last flip-flop is fed to gate G7 of the logic input of previous flip-flop D2. Means each and every output of the next flip-flop is fed back as input or input logic to the previous flip-flop. So two way connections are there. So we will see the working of this. First we will see the shift-right mode. Later we will select the signal-right-left bar as 1. It will allow the circuit to act as right shift mode. So let us take an example. We have to display the output 1011 that is the output at Q0 will be 1, Q1 will be 0, Q2 will be 1 and Q3 will be 1. Now it will enable G1, G2, G3 and G4. As we know the AND gate act as an enable circuit when one of the input is high and in that case the output of that AND gate will be whatever the output we are giving to second terminal. So in this case due to right-left bar 1 we are going to enable gates G1, G2, G3 and G4. So the output of these AND gates are the serial data coming to second terminal. Now in this case the AND gates G5, G6, G7 and G8 are giving the outputs 0. So at first clock cycle we are going to select the input of the given bit stream 1011 and in that we will select the rightmost bit 1. So the input to G1 will be 1 and the output for the flip-flop D0 will be 1. So in this case at clock pulse 1, Q0 will be 1. Now in the second clock pulse the data will be shifted towards right by 1 and the second one will come to output of Q0. At the third clock pulse the data bit will be shifted towards right at D2, D0's data will be at D1 and new data will be at Q0 that is the data is 011 and at the fourth clock pulse all bits are shifted towards right 1 by 1 and finally we will get the data 1011. So this is the tabular form of shift right mode according to the clock pulses and similarly we can show the illustration of shift right operation of BSR. Now we will move towards the shift left mode. Here the reverse procedure will be there, right left bar is provided with input 0. So it allows the whole circuit to act as the shift left mode. So again we will take the input bit as 1011 and we have to display the same bits to Q0 up to Q3 that is 1011. Now we have to select the leftmost bit of this bit stream that is 1. So it will enable now the gates G5, G6, G7 and G8. In this case the gates G1, G2, G3 and G4 will give the output as 0. Now at the first clock cycle the input is given through the serial data input to the gate G8 and here the input is 1. So the output of this AND gate will be 1. Now this output is given to OR gate and which is provided to D flip flop which will result into the output Q3 1. According to the structure the output is fed back to the input logic of previous flip flop. So here in next the bit will be shifted towards left by 1 and the new bit will be appeared at the output Q3. At the third clock pulse the bit is shifted towards left by 1 and the bit of Q3 is shifted towards Q2 and new bit will be appeared at Q3 that is the output will be 1011. Next clock pulse will move the bits towards left by 1 bit and finally we will get the result 1011. Now this is a tabular form of left shift mode according to the clock pulses and serial input given to the inputs input lines. So first we will select here Q3 as we have to move from left right to left. So first we will select here the output Q3 and from Q3 up to Q0 we can show the tabular form like this. Now I will request to stop the video for while and you have to sketch the waveform illustrating shift left mode. Welcome back. So the illustration of shift left mode of BSR can be shown like this. I hope your answer is similar to this. Here are some applications of N-bit BSR. So N-bit BSR can be used in scanning circuit, time delay circuits and calculators and some ICs can be shown here. IC74671 is 4-bit bi-directional shift resistor, IC74HC194 is 4-bit bi-directional universal shift resistor, IC74HC198 is 8-bit bi-directional universal shift resistor. These are some references. Thank you.