CArcMOOC 03.03 - Sequential circuits
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The document covers topics related to sequential circuits and finite state machines (FSMs), including latches, flip flops, and registers. It explains the differences between Mealy and Moore FSMs, providing examples and detailing their functions and state representations. Additionally, the document touches on the concepts of asynchronous versus synchronous circuits.
CArcMOOC 03.03 - Sequential circuits
- 1. Carc 03.03 alessandro.bogliolo@uniurb.it 03. Logic Networks 03.03. Sequential Circuits • Dealing with feedback • Finite state machines • Latches • Flip flops • Registers • Synchronous sequential circuits Computer Architecture alessandro.bogliolo@uniurb.it
- 2. Carc 03.03 alessandro.bogliolo@uniurb.it Dealing with feedback s r y y' 0 0 ? ? 0 1 0 1 1 0 1 0 1 1 0 0 s r y y' y y' 0 0 0 0 1 1 0 0 0 1 0 1 0 0 1 0 1 0 0 0 1 1 0 0 0 1 0 0 0 1 0 1 0 1 0 1
- 3. Carc 03.03 alessandro.bogliolo@uniurb.it Sequential circuits: FSMs • Finite state machines (FSM): (S,I,O,f,g,s0) • Output function o=f(s,i) • Next-state function snext=g(s,i) • Representation: state diagram • Classification: • Combinational f:I O • Sequential (Mealy’s) f:SxI O g:SxI S • Sequential (Moore’s) f:S O g:SxI S • Asynchronous vs Synchronous
- 4. Carc 03.03 alessandro.bogliolo@uniurb.it Moore’s FSM: example ON Light OFF Dark off on offon S = {ON,OFF} I = {on,off} O = {Light,Dark} f: S O g: SxI S state out in f g State Input Output Snext OFF off Dark OFF OFF on Dark ON ON off Light OFF ON on Light ON Case of a simple power supply system controlled by an on/off switch and monitored by a led
- 5. Carc 03.03 alessandro.bogliolo@uniurb.it Mealy’s FSM: example ON OFF off, D on, D off, D test, D on, D test, L S = {ON,OFF} I = {on,off,test} O = {Light,Dark} f: SxI O g: SxI S state in,out f g State Input Output Snext OFF off Dark OFF OFF on Dark ON OFF test Dark OFF ON off Dark OFF ON on Dark ON ON test Light ON Case of a simple power supply system controlled by an on/off switch and monitored by a led when a test button is pressed
- 6. Carc 03.03 alessandro.bogliolo@uniurb.it FSMs: example state input (sr) f g A 00 01 A A 01 01 A A 10 10 B A 11 00 A B 00 10 B B 01 01 A B 10 10 B B 11 00 B
- 7. Carc 03.03 alessandro.bogliolo@uniurb.it Latch SR y y' y' s r f g 0 0 0 1 0 0 0 1 0 1 0 1 0 1 0 0 1 1 0 0 1 0 0 0 1 1 0 1 0 1 1 1 0 1 0 1 1 1 0 0 In order to use the circuit to store a bit, we need three input configurations to: •set y=1 regardless of the current state •set y=0 regardless of the current state •keep y unchanged SETRESET HOLD
- 8. Carc 03.03 alessandro.bogliolo@uniurb.it Latch SR y y' y' s r f g 0 0 0 1 0 0 0 1 0 1 0 1 0 1 0 0 1 1 0 0 1 0 0 0 1 1 0 1 0 1 1 1 0 1 0 1 1 1 0 0 (s,r) = (1,0) SET (s,r) = (0,1) RESET (s,r) = (0,0) HOLD (s,r) = (1,1) NOT ALLOWED Notice that y’=NOTy for all allowed input configurations SETRESET HOLD
- 9. Carc 03.03 alessandro.bogliolo@uniurb.it Flip Flop SR Clk S R s r 0 0 0 0 0 HOLD 0 0 1 0 0 HOLD 0 1 0 0 0 HOLD 0 1 1 0 0 HOLD 1 0 0 0 0 HOLD 1 0 1 0 1 RESET 1 1 0 1 0 SET 1 1 1 1 1 NOT ALLOWED
- 10. Carc 03.03 alessandro.bogliolo@uniurb.it Flip Flop D Level Sensitive Clk D S R s r 0 0 0 1 0 0 HOLD 0 1 1 0 0 0 HOLD 1 0 0 1 0 1 RESET 1 1 1 0 1 0 SET
- 11. Carc 03.03 alessandro.bogliolo@uniurb.it Flip Flop D Edge Triggered n
- 13. Carc 03.03 alessandro.bogliolo@uniurb.it Synchronous Sequential Circuits General Mealy’s Moore’s f(s,i) g(s,i) f(s,i) g(s,i) f(s)g(s,i)