# Chapter 6 Registers and Counters Registers Register and

• Slides: 28

Chapter 6 Registers and Counters

Registers • Register and counter logic circuits contain flipflops • A “register” is a group of flip-flops , each one is capable of storing “ 1 bit” of information • A n-bit register consists of a group of n flipflops capable of storing n bits of binary information. • A “counter” is a register that goes through a sequence of binary states

Registers- four bit register

Register - Four-bit register with parallel load • Additional gates implement 2 -channel mux • Data is always transfer at positive clock pulse • When “Load-input” is “ 1” , the data from inputs transfer to registers • When “Load-input” is “ 0” , the flip-flop output (present state) transfer to register and implement “no change” condition

Register - Four-bit register with parallel load

Shift registers • Shifting of binary information from one cell to its neighboring cell , is called “shift register” • The output of one flip-flop is connected to input of next flip-flop • All flip-flop receive common clock pulses, which shift the data from one stage to the next

Shift registers • The shift can be contro 11 ed with an input by connecting the CLK through an AND gate

Shift registers – serial transfer • The “serial - mode”, transfer and manipulate one bit information at a time • The “parallel – mode”, information is available from all bits of a register and all bits can be transferred simultaneously during one clock pulse

Shift registers – serial transfer

Shift registers – Example

Serial addition(D flip-flop) Parallel adder is a combinational circuit, while serial adder is a sequential one Note : Serial operations are slower compare to parallel operation

Universal Shift Registers The general shift registers have following capabilities: • A clear control to clear the register to 0 • A clock input to synchronize the operation • A shift-right control to enable the shift-right operation • A shift-left control to enable the shift-left operation • A parallel-load control enable, n-input lines associated with the parallel transfer • n parallel output lines • A control state , that leaves the information unchanged

Universal Shift Registers If the register has both shifts and parallel-load capabilities, it is referred to as a universal shift register

Ripple Counters • A register that goes through sequence of states upon application of input pulses is called a “Counter” • A counter that follows the binary number sequence is called a binary counter • A n-bit binary counter consists of n flipflops and counts from 0 through 2ⁿ -1 • Counter are divided into two categories, • Ripple counters • Synchronous counters

Binary Ripple Counter • A 1 goes from 1 to 0, it complements A 2 • A 2 goes from 1 to 0, it complements A 3, and so on for any other higher order • A binary counter with a reverse count is called a binary “countdown counter” • The true output goes from 0 to 1

BCD Ripple Counter • A decimal counter is similar to a binary counter, except that the state after 1001 (the code for decimal digit 9) is 0000 (the code for decimal digit 0)

BCD Ripple Counter

SYNCHRONOUS COUNTERS Binary Counter • If the enable input is 0, a. II J and K inputs are equal to “ 0” and clk does not change the state of the Counter • J and K inputs are equal to 1 if all previous least significant stages are equal to 1 and the count is enabled • A synchronous countdown binary counter goes through the binary states in reverse order, 1 11 1 down to 0000 and back to 11 1 1 to repeat the count

SYNCHRONOUS COUNTERS Up-Down Binary Counter • When the up input is 1, the circuit counts up, since the T inputs receive their signals from the values of the previous normal outputs of the flip-flop • When the down input is 1 and the up input is 0, the circuit counts down, since the complemented outputs of the previous flipflops are applied to the T input • When the up and down inputs are both 0, the circuit does not change state and remains in the same count • When the up and down inputs are both I, the circuit counts up Note: The up input has priority over the down input.