Systems Sequential Circuits Shankar Balachandran* Associate - PowerPoint PPT Presentation

Spring 2015 Week 4 Module 22 Digital Circuits and Systems Sequential Circuits Shankar Balachandran* Associate Professor, CSE Department Indian Institute of Technology Madras *Currently a Visiting Professor at IIT Bombay

Registers  A register is a group of storage cells suitable for holding binary information.  Flip-flop or latches can be used as storage cells in a register. Typically, D flip-flops or latches are used.  There are different types of registers based on the way in which binary data is stored and accessed.  Parallel-in Parallel-out (Data Load)  Serial-in Serial-out (Shift register)  Universal Shift Register Sequential Logic Elements 2

Parallel-In Parallel-Out Register  All cells of a register loaded in one clock cycle. Sequential Logic Elements 3

Parallel Load Loaden_n Sequential Circuits 4

Shift Register  The data is stored by serially sending it in, i.e., n clocks are needed to load an n -bit register. R R R R = Out In 3 2 1 0 t 1 0 0 0 0 0 t 0 1 0 0 0 1 t 1 0 1 0 0 2 t 1 1 0 1 0 3 t 1 1 1 0 1 4 t 0 1 1 1 0 5 t 0 0 1 1 1 6 t 0 0 0 1 1 7 Sequential Logic Elements 5

Different Kinds of Shift Registers in in in Sequential Logic Elements 6

Shift Register  Shift registers can be used to perform multiplication by powers of 2 .  For example, multiplying a binary number by 2 is equivalent to shifting it left by 1 position  Multiplying by 2 i is equivalent to shifting i bit positions to the left and padding the lower significant bits by 0s.  For dividing by powers of 2  Shift right by 1 position  Dividing by 2 i is equivalent to shifting i bit positions to the right and padding the upper significant bits by 0s.  Will lose the reminder though unless the shifted bits are stored also Sequential Logic Elements 7

Parallel Access Shift Register Think about how you will make the flipflops hold the value. They are constantly shifting or loading values now.

Bidirectional Shift Register with Load  All the above register functions can be combined into a single circuit which works as a universal shift register, i.e., bidirectional shift register with parallel load operation: How would you implement universal shift register using D flip-flops and logic gates? Sequential Logic Elements 9

End of Week 4: Module 22 Thank You Sequential Circuits 10