Shift
registers are important components in computers.They act as memories for binary numbers, and are important in shifting
data about the computer.Data may
be received in serial form, i.e. one digit after another, but is sent in whole words
through the computer. Each bit
of a word needs its own wire to travel in, therefore for a 4-byte
word (1 byte = 8 bits, therefore 32 bits) needs 32 parallel connectors.This
is called parallel data transmission.
Very high speeds are possible because of the parallel connectors, buses,
that form the highways between computer components.The diagramshows the difference between serial and parallel data transmission.
Question 5 Why
is the printer cable that comes from a parallel port on a computer is so thick
and heavy? ANSWER
D type flip-flops are
used to enable this in these ways:
Serial
input serial output (SISO)
Parallel
input parallel output (PIPO)
Serial
input parallel output (SIPO)
Parallel
input serial output (PISO)
We will look at a four-bit
serial input parallel output
shift register.
The
resets are all connected so that the circuit can be cleared to 0 at the same
time.
At
the rising edge of the clock input, the output takes on the value of the
data input.
The
set inputs are not connected.
The
Q-bar outputs are not used.
The
Q subscripts refer to the power of 2.Q2
carries the 22 (4) bit.
We are going to put the number 1101
into the register to see how this works and the table below shows the sequence
of events.
Clock
pulse
Q3
Q2
Q1
Q0
Notes
0
0
0
0
0
1
1
0
0
0
2
0
1
0
0
3
1
0
1
0
4
1
1
0
1
Data loaded
5
0
1
1
0
6
0
0
1
1
7
0
0
0
1
8
0
0
0
0
Data out
The
timing diagram is shown here:
We can use the timing
diagram to explain what is happening:
On the clock pulse
F1 changes Q3 from 0 to 1.
This sets F2 to
change Q2 at the second rising edge from 0 to 1.
Which in turn
changes F3 and so on.
F1 changes back
from 1 to 0 on the second rising edge.
followed by F2 and
F3 in turn.
The Table shows the
data being loaded by the 4th clock pulse.
Question
6. Can
you use the timing diagram to explain how a SIPO shift register works? ANSWER
Click HERE
to go on to NAND gate monostables and astables.
We will look at a four-bit
serial input parallel output
shift register.
