Registers are memory elements that store binary words. Counters are registers that count clock pulses. There are different types of registers like buffer registers, shift registers, and controlled shift registers. Ripple counters count clock pulses using JK flip flops but have propagation delays. Synchronous counters clock all flip flops simultaneously, eliminating propagation delays. Ring counters sequentially activate devices by having only one high bit in the stored word.

1. DIGITAL COMPUTER
ELECTRONICS
Third Edition
By Malvino - Brown

2. PART 1: DIGITAL PRINCIPLES
CHAPTER 8: REGISTER AND COUNTERS

3. Registers
 It is the group of memory elements that work together in a unit
 The simplest registers to do nothing more than to store a binary word; other modify the
store word by shifting its bits left or right or by performing other operations
 A Counter is a special kind of register, design to count the number of clock pulses
arriving at inputs
Counters

4. Buffer Register
 It is the simplest kind of registers; all it does is store a digital word
 CONTROLLED BUFFER REGISTER: The same buffer register is provided with active- high

5. Shift Registers
 Shift Register simply moves the stored bits left or right. This bit shifting is essential for
certain arithmetic and logic operations used in micro-computers

7. Controlled Shift Registers
 A controlled Shift Register has control inputs that determines what it does on the next
pulse
 SHL Control
 Feedback
 Left Shift
 Serial Loading: means storing a word in the shift register by entering 1 bit per clock
pulses e.g. 4 bits need 4 clock

8.  Parallel Loading or Broadside Loading: It takes only one clock pulse to store a digital
word

9. Ripple Counters
 It is a register capable of counting the numbers of clock pulses that have arrived at its
clock input
 The circuit shown is built with JK Flip flops; Since the JK inputs are returned to a high
voltage, each flip flop will toggle when its clock input receive a negative edge

11. Ripple Counter
 Ripple Counter: It is known as a Ripple Counter because the carry moves through the
flip flops like a ripple in water. In other word Q0 toggle before Q1, Q1 toggle before Q2,
and so on
 It counts the clock pulses when commanded to do so
 The problem with ripple counters is that each new stage put on the counter adds a
delay. This propagation delay is seen when we look at a less idealized timing diagram
Controlled Ripple Counter
Problems with Ripple Counter

12. Synchronous Counters
 When the carry has to propagate through a chain of n flip flops, the overall
propagation delay time is ntp
 For that very reason the ripple counters are too slow for some applications
 To get around ripple counter we use synchronous counter

13. Working of Synchronous Counters
 However, with the Synchronous Counter, the external clock signal is connected to the
clock input of every individual flip-flop within the Counter so that all of the flip-flops are
clocked together simultaneously (in parallel) at the same time giving a fixed time
relationship. In other words, changes in the output occur in “synchronization” with the
clock signal
 The result of this synchronization is that all the individual output bits changing state at
exactly the same time in response to the common clock signal with no ripple effect
and therefore, no propagation delay

14. Controlled Synchronous Counter
 A low count disable all flip flops. When COUNT is high, the circuit becomes a
synchronous counter; each positive clock edge advance the count by 1

15. Ring Counters
The Ring Counter built with D flip flops

16. Application of Ring Counter
 Ring counters can not compete with ripple and synchronous counters when it comes to
ordinary counting, but they are invaluable when it’s necessary to control a sequence of
operations. Because each ring word has only 1 high bit, you can activate one of the
several devices