Transcript Building D Flip Flops

Building D Flip Flops
• Combinational circuit components
• D Clocked Latch: similar to a flip flop
but simpler
• D flip flop
Galen Sasaki
EE 260 University of Hawaii
1
Combinational Circuit
Components
Voltage
Inverters
Normally
Open Switch
open
L
closed
Galen Sasaki
H
EE 260 University of Hawaii
Normally
Closed Switch
closed
L
open
H
2
D clocked latch
D
Hold
Q
Q
Clock =L
Clock
It similar to a D flip flop
but it reacts to the clock
differently
Load
D
Q
Q=D
Clock = H
Galen Sasaki
EE 260 University of Hawaii
It’s “transparent”
3
Differences between a D flip
flop and a D clocked latch
• D flip flop
– Triggered on positive edge of clock
– Output Q (and state) changes only at a time
instant
• D clocked latch
– Output Q changes (with D) while clock is H
– Output Q changes during a duration of time
– Trickier to use since lots of changes can happen
during a time duration
Galen Sasaki
EE 260 University of Hawaii
4
Building a D clocked latch
Hold
Clock = L
Devices drive
each other
Q
state stored here
Load
Clock = H
Galen Sasaki
Two
configurations
that depend
on the clock
D
Q
EE 260 University of Hawaii
5
Building a D clocked latch
clock
D
Q
clock
clock = L : Hold
clock = H : Load
Galen Sasaki
EE 260 University of Hawaii
6
Building a D flip flop
D
Q
Clock
D
Q
Clock
Clock = L
Load
D-->Q
Hold
Clock = H
Hold
Load
D-->Q
Galen Sasaki
EE 260 University of Hawaii
7
Building a D flip flop
Load
(loads input)
D
Clock
Q
Hold
(output doesnt
change)
D
Clock
Load
(transfers state
to output)
Hold
Q
D
Clock
Q
D
Q
Clock
Input really doesn’t
get stored until the edge
Clock
Galen Sasaki
EE 260 University of Hawaii
8
Summary
• Combinational circuit components
– switches and voltage inverters
• D clocked latch
– Built from switches and voltage inverters
– 2 configurations: load and hold
• D flip flop
– Built from two D latches in series
Galen Sasaki
EE 260 University of Hawaii
9