Vending machine A design-example by Ingo Sander

Transcription

1 Vending machine A design-example by Ingo Sander

2 System ontrol We will design the block System ontrol OIN REEIVER OIN_PRESENT GT_1_EURO EQ_1_EURO LT_1_EURO SYSTEM ONTROL DROP DROP_READY DROP BOTTLE AUMU- LATOR DE_A LR_A RETURN_10_ENT HANGER_READY OIN RETURN Return only 10 cents coin.

3 oin Reciever The System ontrol unit controls a number of subsystems from other suppliers. oin Reciever. Drop Bottle. oin Return. OIN REEIVER OIN_PRESENT GT_1_EURO EQ_1_EURO LT_1_EURO SYSTEM ONTROL AUMU- LATOR DE_A LR_A A AUMULATOR counts up the amount of paid coins. Signal OIN_PRESENT indicates that there are coins and the amount is indicated by the signals GT_1_EURO, EQ_1_EURO, LT_1_EURO. With the signals DE_A and LR_A the systemcontrol unit can reduce the amount by 10 cents, or reset the AUMULATOR.

4 oin Return SYSTEM ONTROL RETURN_10_ENT HANGER_READY OIN RETURN With a pulse on RETURN_10_ENT the coin return unit will eject 10 cent, and signal HANGER_READY when this is done and the unit is ready for the next command.

5 Drop Bottle SYSTEM ONTROL DROP DROP_READY DROP BOTTLE With a pulse on DROP the drop bottle unit will eject a bottle, and signals DROP_READY when this is done and the unit is ready for the next command.

6 Block diagram OIN REEIVER OIN_PRESENT GT_1_EURO EQ_1_EURO LT_1_EURO SYSTEM ONTROL DROP DROP_READY DROP BOTTLE DE_A RETURN_10_ENT OIN RETURN LR_A HANGER_READY Signal properties DROP_READY is active for a clockperiod after the bottle is ejected HANGER_READY is active for a clockperiod after a 10 ent coin is ejected Because of the mechanical properties the following signals are active and inactive for several clock periods: OIN_PRESENT ( active for several clockperiods after the coin is inserted ) DROP_READY ( active for several clockperiods at bottle ejection ) HANGER_READY ( inactive for several clockperiods at coin ejection )

7 Use a Moore-machine State Inputsignals NEXT STATE DEODER STATE REGISTER OUTPUT DEODER Outputsignals lk onstruction of a state machine for the controller of a vending machine Assumptions - Moore-machine - Stateregister implemented with D-flip-flops

8 Function diagram for vending machine Nej no Sum < 1 Reset Myntinkast registrerat? Ja yes Summa? oin input 10 ent, 50 ent, 1 Euro oin return 10 ent Price of one bottle 1 Euro Sum= 1 Sum > 1 Mata ut flaskan Retur 10 ent Nollställ summan Minska summan

9 We draw a state diagram from the functional diagram : State diagram LT _1_ EURO DROP _ READY EQ _1_ EURO DROP _ READY (d) (a) (b) (c) DROP OIN _ PRESENT OIN _ PRESENT OIN _ PRESENT OIN _ PRESENT GT _1_ EURO (f) HANGER _ READY RETURN _10 _ ENT HANGER _ READY (e) LR _ A (g) DE _ A

10 State diagram (a) Wait for coin input (b) Register coin? (c) oin is registered (3 cases) (d) Eject bottle (e) Reset sum (f) Return 10 ent (g) Decrease sum 10 ent

11 Insignals Block schematic State register Outsignals OIN_PRESENT LT_I_EURO D A lk D A DROP EQ_I_EURO RETURN_I0_ENT GT_I_EURO DROP_READY HANGER_READY Next State Decoder D B lk D B Output Decoder LR_A A B D D DE_A lk

12 State encoding Idea: Let the states that are close together in the state diagram have codes with unit distance. (b) next to (c) (d) next to (e) (a) next to (b) (f) next to (g) 7 states 3 state variables A, B, are needed AB a Ø d f 1 b c e g (Ø = don t care) The number of inputs is large, 6, total there may be nine variables in Karnaugh maps???

13 LT _1_ EURO DROP _ READY EQ _1_ EURO DROP _ READY (d) (e) LR _ A B State encoding OIN _ PRESENT (a) 000 OIN _ PRESENT (b) (c) DROP (f) OIN _ PRESENT OIN _ PRESENT GT _1_ EURO HANGER _ READY RETURN _10 _ ENT HANGER _ READY (g) DE _ A A AB a Ø d f 1 b c e g (Ø = don t care) State variable AB, eg. in state (c) is A = 0, B = 1 and = 1

14 oded state table? From the state diagram, you can set up the following coded state table. How do we avoid the complexity of nine variables?

15 Variable-Entered Mapping (VEM) Variable-Entered Mapping can be helpful when you need Karnaugh diagrams with many variables. You write functional expression of Karnaugh diagrams. A + D A AB Ø EQ + GT 0 0 Variables

16 Next state - D A A + D A AB EQ : EQ_1_EURO GT : GT_1_EURO 0 0 Ø EQ + GT A = DA = A B EQ + A B GT + A

17 Next state - D B B + D B AB EQ : EQ_1_EURO P : OIN_PRESENT 0 0 Ø P EQ B = DB = A B EQ + B + B P + A B Easy to miss!

18 Next state - D + D AB P : OIN_PRESENT DR: DROP_READY R: HANGER_READY 0 P Ø DR R = D + A B R + B = A P + B DR

19 Output signals The output signals are the "pulses" which are generated when passing through the states d, f, e, g. DROP = AB LR _ A = AB RETURN _10 _ ENT DE _ A = AB = AB

20 Implementation of the vending machine students must master the the design of simple combinational and sequential digital systems You do that now! When they call from ocaola, it's just for you all Digital Designers to adopt the mission...

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22 What will happen in state Φ? AB a Ø d f 1 b c e g Φ = (010) AB Φ + + A = A B EQ + A B GT + A A (010) AB = 1 1 EQ GT = EQ + GT B + + = A B EQ + B + B P + A B = A P + B DR + A B R + B + (010) AB = 1 1 P DR R = P + DR A B = 1 = 010,110, 011,111 Φ, d, c, e B + ( 010) = 1 1 EQ = 1 AB

23 What will happen in state Φ? A B = 1 = 010,110, 011,111 Φ, d, c, e Φ In Φ-state we are stuck, or we go to (c) and then on. Or we go to (d) and offers soft drinks, or we go to (e) and resets any previous payment. Obviously, we need to purchase a reset circuit that ensures that the machine always starts in (a) 000! Otherwise we will have legitimate complaints from the customers! RESET-generator

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