Shift Registers

1
Shift Registers

• Kleitz, Chapter 13
• Parallel Serial Conversion

2
Shift Register

• A circuit to move and store data bits.
• Can be used for
• serial ltgt parallel conversions

3
Parallel - Serial Conversion
Parallel
Serial
Parallel
4
Demonstration Serial to Parallel Conversion

• Need volunteers
• 8 datum
• 4 flip-flops
• 1 clock

5
Serial to Parallel Conversion
Parallel Data Out
Serial Data In
1
1
1
Q1
Q0
Q2
StrobeClock
6
Serial to Parallel Conversion

• At each clock pulse
• Input D changes to next Data
• use a D flip flop
• State of left flip-flop is transfered to next
  right flip-flop
• after correct number of pulses (3 in example)
• read the parallel data at
• MSB Q2, Q1, LSB Q0

7
Strobe Input

• Strobe is put into an and gate with the clock
• acts as an enable signal
• Prevents shift progress
• Holds parallel data

8
S to P Progress of Data
Serial Data D2 D1 D0
Parallel Data
9
J-K Parallel to Serial
Parallel Data In (Active Low) D2 D1 D0
Q1
Q0
Serial Out
Q2
0
1
10
Demonstration Serial to Parallel

• Data
• side by side one side step left at clocks
  command of pulse.
• After four pulse commands clock says strobe
• All step forward for parallel read.
• flip-flops
• arms gate
• at each pulse command, lift arm allowing 1
  datum to move out or in.

11
Shift Register Example

• Build 3-bit register from J-K FF.
• Inputs Data to Set
• set command loads data.
• use NAND set NAND data
• Clock shifts data to right.
• See Multisim.

12
Multisim Shift Register
13
Goal

• Convert 011 parallel to serial
• D2 0, D1 1, D0 1
• Q0 serial output

14
Parallel to Serial Conversion
Set Data
Reset
Ready for next cycle
1
0
2
Cp RD Q0 Q1 Q2
LSB
MSB
15
Sequence Clock Pulse 1

• Q2 gt 0
• reset by fixed K2 1, J2 0
• Q1 gt 0
• reset by K1 Q2, J10
• Q0 gt 1
• set by J0Q11

16
Sequence Clock Pulse 2

• Q2 gt 0
• kept reset by fixed K2 1, J2 0
• Q1 gt 0
• kept reset by K1 Q2, J10
• Q0 gt 0
• reset by K0Q11

17
Serial Data

• Observe
• first output to appear on Q0 was LSB
• LSB sent first
• Timing diagram starts from t0 at left side.