REGISTERS AND COUNTERS Flashcards
(31 cards)
What are the classifications according to function of circuits that include flipflops
Registers
Counters
Describe registers and give an example
A register is a group of binary cells.
An n ‐bit register consists of a group of n flip‐flops sharing a common clock and capable of storing n bits of binary information.
Internal registers used in microprocessors to manipulate data
Describe counters and give an example
Counters: A register that goes through a predetermined sequence of binary states.
Counters are a special type of register
The gates in the counter are connected in such a way as to produce the prescribed sequence of states.
PC (program counter) in microprocessors
What is the purpose of the flip-flops and gates in a register
A register consists a group of flip-flops and gates that
effect their transition.
The flip-flops hold the binary information.
The gates determine how the information is transferred into the register.
What are registers used for
simple data storage
data movement
processing operations
Illustrate an 8-bit register
*See page 4 and 5
Do the questions about 2-bit Register on page 6
**
Describe and illustrate the making of a 4-bit register
The register here is constructed with four
D-type flip-flops.
*See page 7
Explain the use of clear and clock in the 4-bit register
“Clock” triggers all flip-flops on the positive edge of each pulse.
“Clear” is useful for clearing the register to all 0’s prior to its clocked operation.
The R inputs must be maintained at logic 1 (i.e., de-asserted) during normal clocked operation.
Is it possible to use the diagram/state table model to design registers
Due to the large numbers of states and input combinations as n becomes large, the state diagram/state table model is not feasible!
What are methods we can use to design registers?
Add predefined combinational circuits to registers
Example: To count up, connect the register flip-flops to an incrementer
Design individual cells using the state diagram/state table model and combine them into a register
A 1-bit cell has just two states
Output is usually the state variable
Discuss register storage in terms of expectations, the reality and possible ways to realize the expectations
Expectations:
A register can store information for multiple clock cycles
To “store” or “load” information should be controlled by a signal
Reality:
A D flip-flop register loads information on every clock cycle
Realizing expectations:
Use a signal to block the clock to the register,
Use a signal to control feedback of the output of the register back to its inputs, or
Use other SR or JK flip-flops, that for (0,0) applied, store their state
What is load in register storage
Load is a frequent name for the signal that controls register storage and loading
Load = 1: Load the values on the data inputs
Load = 0: Store the values in the register
Describe and illustrate Registers with Clock Gating and the logic needed for it
The Load signal enables the clock signal to pass through if 1 and prevents the clock signal from passing through if 0.
Logic:
Gated Clock = Clock + Load
*See page 10 for illustrations
Describe Registers with Load-Controlled Feedback
A clock edge applied to the C inputs of the register of will load all inputs in parallel.
For synchronism, it is advisable to control the operation of the register with the D inputs rather than controlling the clock in the C inputs of the flip-flops.
Loading a register: transfer new information into the register. Requires a load control input.
Parallel loading: all bits are loaded simultaneously.
What is a more reliable way to selectively load a register and give an example using a 2-bit register
Run the clock continuously, and
Selectively use a load control to change the register contents.
Example
For Load = 0, loads register contents (hold current values)
For Load = 1, loads input values (load new values)
Hardware more complex than clock gating, but
free of timing problems
*See page 12 for illustration
Describe and illustrate a 4-bit Register with Load Control:
When the load input is 1, the data in the four inputs are transferred into the register with next positive
edge of the clock.
When the load input is 0 ,the outputs of the flip-flops are connected to their respective inputs.
The feedback connection from output to input is
necessary because the D flip-flops does not have a “no change” condition.
*See page 13
Do the example on page 13 on Using Registers to Implement Sequential Circuits
*
What are the different data formats of registers
Serial
Parallel
Describe the classifications of registers
Input/Output
SISO – Serial Input Serial Output
SIPO – Serial Input Parallel Output
PISO – Parallel Input Serial Output
PIPO – Parallel Input Parallel Output
Application
Shift Registers
Storage Registers (e.g. PIPO)
Describe shift registers
Shift register is register capable of shifting its binary information in one or both direction
Capable of shifting the binary information held in each cell to its neighboring cell, in a selected direction
Consists of a chain of flip‐flops in cascade, with the output of one flip‐flop connected to the input of the next flip‐flop
Illustrate and describe how shifting happens in shift registers
All flip-flops receive common clock pulses, which activate the shift from one stage to the next.
Each clock pulse shifts the contents of the register one bit position to the right.
The serial input determines what goes into the leftmost flip-flop during the shift.
The serial output is taken from the output of the rightmost flip-flop.
*See page 17
Illustrate the 7 basic data movements in shift registers
*See page 18
Complete the table on page 19
*See page 19
