Page 214 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Unit 11: Registers and Counters

• Each of plural logic gates has two input terminals each of which is connected to an output Notes
of a predetermined step of the shift register, so that an output signal outputted from each
logic gate to the corresponding driving circuit for an operating device constitutes timing
signal carrying information including starting and terminating times of operation.

• The need for memory address decoding arises from the fact that the main memory of a
computer system is not constructed from a single component, which uniquely addresses
each possible memory location.
11.7 Keywords

Random access memory: This is the place in a computer where the operating system, application
programs, and data in current use are kept so that they can be quickly reached by the computer’s
processor.
Read-only memory: This is a form of semiconductor memory technology used where the data is
written once and then not changed.

Ring counters: These are implemented using shift registers and it is essentially a circulating shift
register connected so that the last flip-flop shifts its value into the first flip-flop.
Ripple counter: It is easy to understand. Each stage acts as a Divide-by-2 counter on the stage’s
signal.
Semiconductor memory: This technology is an essential element of today’s electronics. Normally
based around semiconductor technology, memory is used in any equipment that uses a processor
of one form or another.
Synchronous binary counter: This counts from 0 to 2 – 1, where N is the number of bits/flip-
N
flops in the counter.
Synchronous dynamic random access memory (SDRAM): The SDRAM, this form of semiconductor
memory can run at faster speeds than conventional DRAM.

1. Design a 4.bit parallel-in/parallel-out register with loading information in
one asynchronous stage.
2. Design a 4.bit maximum length shift register counter.

11.8 Review Questions

1. Using D-flip-flops and waveforms explain the working of a 4-bit SISO shift register.

2. What is a shift register? Can a shift register be used as a counter? If yes, explain how.
3. Explain ripple counter in detail.
4. Describe the synchronous counters. Explain with circuit diagram.
5. What do you understand by 4-bit parallel-access shift register?
6. Explain
(a) Partial Address Decoding
(b) Full Address Decoding
7. What are the semiconductor memories? Also describe the types of semiconductor memory.
8. Describe the semiconductor memory technologies.

9. What is block address decoding?
10. Describe the partial address decoding.

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