Introduction Data formats Buffer registers Shift registers Serial In Serial Out Serial In Parallel Out Parallel In Serial Out Parallel In Parallel Out

1. REGISTERS
By
SHASHI LATA
ASSISTANT PROFESSOR
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2. CONTENTS
• Introduction
• Data formats
• Buffer registers
• Shift registers
• Serial In Serial Out
• Serial In Parallel Out
• Parallel In Serial Out
• Parallel In Parallel Out
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3. Introduction
• Flip-flop is a 1 bit memory cell which can be
used for storing the digital data.
• To increase the storage capacity in number of
bits, we have to use a group of flip-flops. Such
a group of flip-flops is known as a register.
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4. Data formats
• The data can be entered in serial (one bit at a
time) manner or in the parallel form (all the bits
at the same time) into a register. And the stored
data can be retrieved in the serial or parallel
form.
• Modes of operation:
– Serial In Serial Out (SISO)
– Serial In Parallel Out (SIPO)
– Parallel In Serial Out (PISO)
– Parallel In Parallel Out (PIPO)
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5. Buffer registers
• Let us assume that the word to be stored is B3, B2 B1 B0 = 1
0 1 0.
• These bits are connected to the D inputs of the four D flip-
flops.
• Then the clock pulse is applied.
• Corresponding to the first negative edge of the clock pulse,
the outputs of all the D flip-flops will follow their
respective inputs.
– Q3 Q2 Q1 Q0 = B3, B2 B1 B0 = 1 0 1 0
• Even if the inputs are now changed, the output remains
latched to 1 0 1 0 till the next negative edge of the clock
arrives at the input.
• Thus the buffer register is capable of storing the digital data
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6. Buffer registers
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7. Shift Registers
• The binary data can be moved within the
register from one F-F to the Other or outside it
with the applications of clock pulses
• The registers that allow such data transfer are
called shift registers.
• These are used for data storage, data transfer
and arithmetic and logical operations.
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8. Types of Shift Registers
• Serial input Serial Output (SISO)
• Serial Input Parallel Output (SIPO)
• Parallel In Serial Out (PISO)
• Parallel In Parallel Out (PIPO)
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9. Serial input Serial Output (left mode)
• Let all the Flip-flops be initially in the reset
condition, i.e., Q3=Q2=Q1=Q0 = 0
• We are going to illustrate the entry of a four bit
binary number 1 1 1 1 into the register.
• When this is to be done, this number should be
applied to Din bit-by-bit with the MSB bit applied
first.
• The D input of FF-0 i.e. D0 is connected to serial
data input (Din), output of FF-0i.e. Q0 is applied
to the input of next FF i.e. D1 and so on.
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10. Serial input Serial Output (left mode)
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11. SHIFT LEFT OPERATION
CLK Q3 Q2=D3 Q1=D2 Q0=D1 SERIAL
INPUT
Din=D0
0 0 0 0
0 0 0 1 1
0 0 1 1 1
0 1 1 1 1
1 1 1 1 1
DIRECTION OF DATA TRAVELwww.advanced.edu.in

12. Serial input Serial Output (Right mode)
• Let all the Flip-flops be initially in the reset
condition, i.e., Q3=Q2=Q1=QO = 0
• We are going to illustrate the entry of a four bit
binary number 1 1 1 1 into the register.
• When this is to be done, this number should be
applied to ‘Din’ bit-by-bit with the LSB bit applied
first.
• The D input of FF-3 i.e. D3 is connected to serial
data input (Din), output of FF-3,i.e. Q3 is applied
to the input of next FF i.e. D2 and so on.
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13. Serial input Serial Output (Right mode)
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14. SHIFT RIGHT OPERATION
CLK DIN=D3 Q3=D2 Q2=D1 Q1=D0 Q0
0 0 0 0
1 1 0 0 0
1 1 1 0 0
1 1 1 1 0
1 1 1 1 1
DIRECTION OF DATA TRAVEL
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15. Serial Input Parallel Output (SIPO)
• In this, data is entered serially and taken out
in parallel form.
• That means first the data is loaded bit-by-bit.
The outputs are disabled as long as the data is
being loaded.
• As data is loaded, the output data is enabled
over all the output lines simultaneously.
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16. Serial Input Parallel Output (SIPO)
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17. Parallel In Serial Out (PISO)
• In this mode, bits are entered in parallel, i.e.,
simultaneously into a shift register.
• Output of previous flip-flop is connected to
the input of the next one via a combinational
circuit.
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18. Parallel In Serial Out (PISO)
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19. Parallel In Parallel Out (PIPO)
• The four bit binary input B0 B1 B2 B3 are applied
to the data inputs D0 D1 D2 D3 respectively of
the four flip-flops.
• As soon as the negative clock edge is applied, the
input binary bits will be loaded into the flip-flop
simultaneously.
• The loaded bits will appear simultaneously to the
output side. Only one clock pulse is essential to
load all the bits. Therefore PIPO mode is the
fastest mode of operation.
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20. Parallel In Parallel Out (PIPO)
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21. SUMMARY
• Registers are the devices that can store bits
using bit-storage devices known as flip-flops.
• These can be stored by shifting data bits in
series or in parallel.
• The clock bits play a key role in the shifting
process of registers.
• Parallel In Parallel Out mode is the fastest
mode of operation as it requires a single clock
bit.
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22. SHASHI LATA
ASSISTANT PROFESSOR
shashi_fbd@rediffmail.com
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70 km Milestone,
Delhi-Mathura Road, Dist. Palwal, Haryana-
121105
Enquiry No: +91–1275–398400, 302222
Tele Fax: +91-1275-398406
E-mail: info@advancedinstitutions.com
Website: www.advanced.edu.in
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