bruce mayer, pe licensed electrical & mechanical engineer bmayer@chabotcollege
DESCRIPTION
Engineering 43. Sequential ( FlipFlop ) Logic. Bruce Mayer, PE Licensed Electrical & Mechanical Engineer [email protected]. But First… WhiteBoard Work. For the Truth Table Shown at right Construct the Karnaugh Map Write The Minimized Function Q(A,B,C,D) Draw the Logic Circuit - PowerPoint PPT PresentationTRANSCRIPT
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx1
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Bruce Mayer, PELicensed Electrical & Mechanical Engineer
Engineering 43
Sequential (FlipFlop)
Logic
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx2
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
But First… WhiteBoard Work For the Truth Table
Shown at right• Construct the Karnaugh
Map• Write The Minimized
Function Q(A,B,C,D)• Draw the Logic Circuit
Notice “1’s” in Rows• 1, 5, 9, 13, 14, 15
– Need only put “1’s” in these locations; other cells Assumed to be Zero
Row A B C D Q0 0 0 0 0 01 0 0 0 1 12 0 0 1 0 03 0 0 1 1 04 0 1 0 0 05 0 1 0 1 16 0 1 1 0 07 0 1 1 1 08 1 0 0 0 09 1 0 0 1 110 1 0 1 0 011 1 0 1 1 012 1 1 0 0 013 1 1 0 1 114 1 1 1 0 115 1 1 1 1 1
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx3
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Blank Map (NonStretching)
AB\CD 00 01 11 10
00
01 1
11
10
AB\CD 00 01 11 10
00 A’B’C’D’ A’B’C’D A’B’CD A’B’CD’
01 A’BC’D’ A’BC’D A’B’CD A’B’CD’
11 ABC’D’ ABC’D ABCD ABCD’
10 AB’C’D’ AB’C’D AB’CD AB’CD’
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx4
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Stretchable Blank Map
AB\CD 00 01 11 10
00
01
11
10
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx5
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
More… WhiteBoard Work Implement This Function using ONLY
NAND Gates
An Example of NAND-Gate Synthesis• NANDS are easier to construct than
ANDs, ORs, NORs – NANDs are the preferred gate for logic circuits
BADCBADCAF
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx6
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
“Memory Filled” Logic The Invert/AND/OR Combinatorial
Logic Circuits depended ONLY on the Current Inputs; previous states did Not affect the Current State• Combinatorial Logic is MEMORYLESS
In SEQUENTIAL Logic the Circuit Output CAN Depend on the Previous condition of the Circuit• Sequential Logic has MEMORY
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx7
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Sequential Circuit A sequential circuit
consists of a feedback path, and employs some memory elements
[Sequential circuit] = [Combinational logic] + [Memory Elements]
Combinational logic
Memory elements
Combinational outputs Memory outputs
External inputs
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx8
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Synchronous vs Asynchronous Almost all Logic “Chips” Include a Clock The Clock helps to “Synchronize” the
Operation of the Circuits. The “Clock” is simply a very regular Hi/Lo
Pulse train Logic Forms are divided into two groups:
• SYNCHRONUS → Depend on Clock• Asynchronous → NO Clock-Dependency
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx9
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Asynchronous S-R FlipFlop Cross-coupled NOR gates
• Similar to inverter pair, with capability to force Q to 0 (reset=1) or 1 (set=1)
R
S
Q
Q'RS
Q01
0 1
R
S
Q
Q'
10
1 0
R
S
Q
Q'
n-10
0 n-1
R
S
Q
Q'
??1
1 ??
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx10
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
NAND based SR FlipFlop Cross-coupled NAND gates
• Similar to inverter pair, with capability to force Q to 0 (reset=0) or 1 (set=0)
R'S' Q Q
Q'
S'
R'
NOR notes Any HI input → LO output
• Any HI → LO All LO inputs → HI output
• All LO → HI
Any LO input → HI output• Any LO → HI
All HI inputs → LO output• All HI → LO
NAND notes
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx11
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
State Behavior of SR FlipFlop Transition Table
Sequential (output depends on history when inputs R=0, S=0) but asynchronous
R
S
Q
Q'
S R Qn-1 Qn 0 0 0 00 0 1 10 1 0 00 1 1 01 0 0 11 0 1 11 1 0 X1 1 1 X
hold
reset
set
not allowed
characteristic equationQn = S + R’ Q∙ n-1
Qn-1\SR 00 01 11 10
0 0 0 X 1
1 1 0 X 1
SETREset
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx12
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
SR FlipFlop Timing Behavior
Reset Hold Set SetReset Race
R
S
Q
Q’
100
R
S
Q
Q'
“Races” Produce UnPredictable OutPuts
Any HI input → LO output• Any HI → LO
All LO inputs → HI output• All LO → HI
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx13
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Clocked SR FlipFlop Control times when
R and S inputs matter• Otherwise, the slightest glitch on R or S while
enable is low could cause change in value stored• Ensure R & S stable before utilized (to avoid
transient R=1, S=1)
enable'S' Q'
QR' R
S
Set Reset
S'R'enable'QQ'
100
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx14
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Clocked SR FlipFlops NOR-NOR
Implementation
TruthTable
• For NOR: any-Hi→LO; ALL-LO→Hi
enable'S' Q'
QR' R
S
R’ S’ En’ R S Qn
0 0 0 1 1 NotAllowed0 1 0 1 0 Reset to 01 0 0 0 1 Set to 11 1 x 0 0 Qn−1
x x 1 0 0 Qn−1
x → Don’t Care
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx15
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Clocked SR FlipFlops NAND-NOR
Implementation
TruthTable
R S C Qn
0 0 x Qn−1
0 1 1 Set to 11 0 1 Reset to 01 1 1 NotAllowedx x 0 Qn−1
x → Don’t Care
Circuit Symbol
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx16
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
SR FlipFlop Clock-Overide Sometimes Need to Set or Reset the
FlipFlop withOUT Regard to the Clock
Note the position of Pr & Cl on the 3rd-Stage ORs (any Hi→Hi)• Ensures Pr & Cl OverRide R, S, & C
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx17
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Edge Triggered D FlipFlop sensitive to
inputs only near edge of clock signal (not while steady )
Q
D
Clk=1
R
S0
D’
0
D’ D
Q’
holds D' whenclock goes low
holds D whenclock goes low
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx18
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Edge-Triggered FlipFlop Flavors POSITIVE edge-triggered
• Inputs sampled on RISING edge; outputs change after RISING edge
NEGATIVE edge-triggered flip-flops• Inputs sampled on falling edge; outputs change
after falling edge
positive edge-triggered FF
negative edge-triggered FF
DCLK
QposQpos'QnegQneg'
100
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx19
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Edge Triggered D FlipFlop 4-NAND,
1-NOTimplementation
Truth Table for All Postive-GoingEdge D-FF’s• NAND:
– any LO → Hi– All HI → LO
CLK D Qn
0 x Qn−1
1 x Qn−1
↑ 0 0↑ 1 1
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx20
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Edge Triggered JK FlipFlop A “Toggling” Flip Flop
• Under A certain Control-Set: Q → Q’– Notice that Q does NOT go HI-for-sure or
LO-for-sure, and it does NOT remain STEADY
A NAND Nest:• Circuit Symbol
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx21
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
JK FlipFlop Toggle TruthTable The Simplified Ckt
Note that the outputs feed back to the enabling NAND gates. This is what gives the toggling action when J=K=1
ReCall NAND• Any LO → Hi• ALL Hi → LO
C J K Qn Notes0 x x Qn−1 No Chg1 x x Qn−1 No Chg↓ 0 0 Qn−1 No Chg↓ 0 1 0 Reset to 0↓ 1 0 1 Set to 1↓ 1 1 Q’n−1 TOGGLE
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx22
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Cascading FF → Shift Register Serial-in/Parallel-out Shift register
• New value goes into first stage• While previous value of 1st stg goes into 2nd stg• The QN can be SAMPLED any time
CLK
INQ0 Q1
D Q D Q OUT
IN
Q0
Q1
CLK
100
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx23
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Example: Eliminate Inconsistency
D Q
D Q
Q0
Clock
Clock
Q1
Async Input
Clocked Synchronous
System
is asynchronous and fans out to D0 and D1
one FF catches the signal, one does not
inconsistent state may be reached!
In
Q0
Q1
CLK
D Q
D Q
Q0
Clock
Clock
Q1
Async Input D Q
Synchronizer
Want to Send SAME
Input Value to
TWO Places
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx24
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
FlipFlops Summarized Development of D-FF
• Level-sensitive used in custom integrated circuits– can be made with 4 pairs of gates– Usually follows multiphase non-overlapping
clock discipline• Edge-triggered used in programmable logic
devices– Good choice for data storage register
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx25
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
FlipFlops Summarized Historically J-K FF was popular but now
never used• Similar to R-S but with 1-1 being used to
toggle output (complement state)• Same Operation Can always be
implemented using D FlipFlops Preset and Clear inputs are highly
desirable on flip-flops• Used at start-up or to reset system to a
known state
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx26
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
FlipFlops Summarized Reset (set state to 0) R
• Synchronous: Dnew = R' • Dold – Transition only when next clock edge arrives
• Asynchronous: doesn't wait for clock, – quick but dangerous
Preset or Set (set state to 1) S• Synchronous: Dnew = Dold + S
– Transition only when next clock edge arrives)• Asynchronous: doesn't wait for clock
– quick but dangerous
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx27
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
WhiteBoard Work Use Gates and a D-
FF to Implement the JK-FF operation
C J K Qn Notes0 x x Qn−1 No Chg1 x x Qn−1 No Chg↓ 0 0 Qn−1 No Chg↓ 0 1 0 Reset to 0↓ 1 0 1 Set to 1↓ 1 1 Q’n−1 TOGGLE
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx28
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
All Done for Today
IEEE91-1984Gates
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx29
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
Bruce Mayer, PELicensed Electrical & Mechanical Engineer
Engineering 43
AppendixLogic Syn
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx30
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
RowA
BC
DQ
00
00
00
10
00
11
20
01
00
30
01
10
40
10
00
50
10
11
60
11
00
70
11
10
81
00
00
91
00
11
101
01
00
111
01
10
121
10
00
131
10
11
141
11
01
151
11
11
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx31
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx32
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
NAND Gate Synthesis With the expression in SOP form
1. After any need inversions; In the first logic level there are as many logic gates as terms in the SOP expression
2. Each gate corresponds to a SINGLE Term, and has, as inputs, the variables in that term
3. The outputs of the First Logic-Level are ALL inputs to a SINGLE (multi-input if needed) NAND gate
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx33
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx34
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx35
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx36
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx37
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx38
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx39
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx40
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis
[email protected] • ENGR-43_Lec-05c_Thevenin_AC_Power.pptx41
Bruce Mayer, PE Engineering-43: Engineering Circuit Analysis