Lesson 1. The screen and car A: a lift that goes by its buttons

After this lesson the house has one car: you press buttons on its panel — it moves, opens its doors at the right floors, rings a chime and decides by itself where to go next: first all the floors in one direction, then it turns around. The screen shows where the car is, whether its doors are open, which buttons are pressed and where it is going.

1.1. The idea: the car is a machine with memory

The car remembers four things:

• where it is — the position, 5 bits: the floor (3 bits) and the step between floors (2 bits);
• where it goes — the direction, 1 bit;
• whether the doors are open — a timer, 3 bits;
• which buttons are pressed — 8 latches.

Once a cycle (Clock 2Hz, half a second) the machine looks at all of this and decides: stand, open the doors, go up or down. The car passes a floor in 4 cycles — 2 seconds, and keeps its doors open for 2 seconds too.

1.2. The idea: one way while there is somewhere to go

The rule of real lifts: keep going one way and stop at every pressed floor on the way; you may turn around only when no pressed buttons are left ahead. For that the car needs two facts:

• UPR — a pressed button above the car;
• DNR — a pressed button below.

"Above" and "below" come from OR chains — a thermometer: for a car at the 4th floor "above" is 5, 6, 7, 8 and "below" is 1, 2, 3. The decision at a floor:

• up: UPR AND (going up OR NOT DNR);
• down: DNR AND (going down OR NOT UPR).

1.3. The idea: a button is a latch, not a flip-flop

A button is pressed for a fraction of a second, and a cycle is half a second: a flip-flop that stores only on the edge would miss the press. So the button sets a latch at once. Three things clear it: the doors opened at this floor, the Cancel button (it clears all the car buttons at once) and reset. Pressed the wrong floor — Cancel, then the right one.

1.4. Building

A new project. You need the gates NOT, NAND, NOR, AND, OR, XOR: already in the library from another kit of the series — take them; want to build from scratch — lesson 0; straight to the point — paste lesson 0 (Cmd+I).

Step 1. Chip SRLatch — latch: S stores 1, R stores 0

If SRLatch is already in the library (from another kit of the series), skip this step.

Ctrl+G → name SRLatch. Legs: inputs R, S; outputs Q, nQ.

Step 2. Chip DLatch — data latch

If DLatch is already in the library (from another kit of the series), skip this step.

Ctrl+G → name DLatch. Legs: inputs D, EN; outputs Q, nQ.

Step 3. Chip DFF — flip-flop: stores D on the CLK edge

If DFF is already in the library (from another kit of the series), skip this step.

Ctrl+G → name DFF. Legs: inputs D, CLK; outputs Q, nQ.

Step 4. Chip FA — full adder

If FA is already in the library (from another kit of the series), skip this step.

Ctrl+G → name FA. Legs: inputs A, B, CI; outputs S, CO.

Step 5. Chip MUX2 — one of two

If MUX2 is already in the library (from another kit of the series), skip this step.

Ctrl+G → name MUX2. Legs: inputs A, B, S; outputs Y.

Step 6. Chip AND3 — AND with 3 inputs

If AND3 is already in the library (from another kit of the series), skip this step.

Ctrl+G → name AND3. Legs: inputs A, B, C; outputs Y.

Step 7. Chip OR3 — OR with 3 inputs

If OR3 is already in the library (from another kit of the series), skip this step.

Ctrl+G → name OR3. Legs: inputs A, B, C; outputs Y.

Step 8. Chip OR4 — OR with 4 inputs

If OR4 is already in the library (from another kit of the series), skip this step.

Ctrl+G → name OR4. Legs: inputs A, B, C, D; outputs Y.

Step 9. Chip OR8 — OR with 8 inputs

If OR8 is already in the library (from another kit of the series), skip this step.

Ctrl+G → name OR8. Legs: inputs A, B, C, D, E, F, G, H; outputs Y.

Step 10. Chip DEC8 — decoder 3 → 8: exactly one of eight wires is lit

If DEC8 is already in the library (from another kit of the series), skip this step.

Ctrl+G → name DEC8. Legs: inputs I0, I1, I2; outputs Y0, Y1, Y2, Y3, Y4, Y5, Y6, Y7.

Step 11. The screen: the picture and 152 legs

Segment LCD from the palette, ⚙ → ⬆ → project/lift/screen/lift-screen.png (88 × 130 dots). Turn on Ghost. Marking: S, click a blob (the wand), Enter, the name, Enter — a leg appears on the body, a label with its name next to it. Each segment is one blob, one click. The shaft letters, floor numbers and walls are the background — do not mark them.

Mark the whole screen at once, all three shafts: the legs of shafts B and C, the ▶ and the call squares are not connected yet and stay dark — their wires come in lessons 2–4. Digit segments: a is the top, then clockwise, g is the middle.

Step 12. Power, clock, reset

Clock — click the body up to 2Hz: a cycle is half a second, the car passes a floor in 4 cycles (2 seconds) and keeps the doors open for 4 cycles. RST is the reset switch; nR is its inverse, it stands in front of every flip-flop.

Step 13. Car A panel

Eight floor buttons and Cancel. Put them in a column to the right of the screen, «8» on top: this is the panel inside car A. Press them with the mouse.

Step 14. Where the car is

The position is 5 bits: p4 p3 p2 is the floor (0–7, on the screen 1–8), p1 p0 is the step between floors. atF = 1 when the step is 0: the car stands exactly at a floor. DEC8 lights one wire y0–y7 — the floor of the car.

Step 15. Doors open

The door timer t2 t1 t0 (step «Door timer»): while it is not 0, the doors are open (OPEN).

Step 16. Car at a floor

AC<f> — the car stands at floor f: this is also the frame on the screen. O<f> — the doors are open at floor f: it clears the button of this floor.

Step 17. Car buttons — latches

A button is pressed for a fraction of a second, and a cycle is half a second: a flip-flop would miss the press. So the button sets a latch SRLatch at once. kr<f> clears the latch: the doors are open at this floor, or Cancel (kc — it clears all eight), or reset. While it is being cleared, a press does not get through: a latch must not get S and R together. The AK<f> output is the dot to the right of the shaft.

Step 18. The thermometer: what is below, what is above

a<f> = 1 if the car is below floor f; b<f> = 1 if it is above. These are OR chains from the lit y: for a car at the 4th floor a5, a6, a7 and b0…b2 are lit. For the 1st and 8th floor y0 and y7 themselves are enough.

Step 19. Work above? Below?

UPR — a pressed button above the car: the OR of «button f AND the car is below f». DNR — the same downwards.

Step 20. The button of this floor

hK — the button of the floor where the car is, is pressed. gOK — «going down or nothing above»: it is used in the decision and in lesson 2.

Step 21. Here: stop

here — we stand at a floor, the doors are closed, the button of this floor is pressed: open the doors. It also rings the chime (the last step).

Step 22. Decision: up or down

At a floor (doors closed, nothing to do here) the car decides: up if there is work above and (we go up or nothing below); down — the other way round. Keep going one way while there is work there, and only then turn around.

Step 23. Direction

At a floor the direction is decided again (mvUp; no work — «down»), on the way and with open doors it is kept. Flip-flop dir: 1 means up.

Step 24. Moving

go — move on this cycle: between floors always (a lift does not stop mid-shaft), at a floor if we decided to go.

Step 25. Position counter

Five FA add +1 (up) or 11111 (that is −1: down) to the position — or 0 when standing. AND with nR — reset to the 1st floor.

Step 26. Door timer

Opened (here) — 4 (100), open — minus 1 (three FA add 111), closed — 0. The doors stay open for 4 cycles — 2 seconds.

Step 27. Arrows

An arrow is lit while there is work or the car is moving: ▲ — direction up, ▼ — down.

Step 28. The screen: door leaves, bar, digit

AD<f> — the door leaves: the car is at floor f and the doors are closed. AM<f> — the car is on the way between floors f and f+1. The floor digit comes from the one lit y: a segment is lit on the floors where it is needed (a — on 2, 3, 5, 6, 7, 8 …), so each segment is one OR.

Step 29. Chime

Speaker from the palette: click the icon on the left — «buzzer» mode, the grille — tone 880. It rings while the doors are opening (here).

1.5. Check

Do not fold the board — in lesson 2 the floor call buttons are added to it.

1. RST on and off. On the screen in shaft A: the car is at the 1st floor — a frame with door leaves (doors closed), digit 1 above the shaft, no arrows.
2. Press 5. A dot lights to the right of the shaft at the 5th floor, ▲ above the shaft. The car moves: the frame goes out, a bar is lit between floors, the digit grows 1 → 2 → 3 → 4. After 8 seconds the car is at the 5th: the chime rings, the frame is empty (doors open), the dot goes out, ▲ goes out. 2 seconds later the leaves appear — the doors closed.
3. Press 7, 8 and 3. The car goes up: opens its doors at the 7th, then at the 8th, then ▼ — and goes down to the 3rd. It would not go to the 3rd on the way up: first all the work in one direction, then the turn.
4. Press 6, then Cancel, then 5. The dot at 6 goes out, the car goes to the 5th.
5. Press 1 and, while the car moves, — Cancel. The car reaches the nearest floor and stops without opening its doors: a lift does not stop mid-shaft.
6. The car stands with closed doors — press the button of its floor: the doors open at once. While the doors are open, the button of this floor does not light.

Lesson 1 paste (Cmd+I)

You need the gates NOT, NAND, NOR, AND, OR, XOR (lesson 0 or its paste) and the parts of steps 1–10 (SRLatch … DEC8) — they are at the start of the paste; if they are already in the library, delete their chip blocks. The screen (Segment LCD) and the chime tone are done by hand, steps 11 and 29.

# Lesson 1 — the screen and car A: position, car buttons and Cancel, doors, up / down / here.# Paste: Cmd+I into a project with the gates. Segment LCD and Clock 2Hz — by hand. # ---------- parts (if already in the library, delete their blocks) ---------- chip SRLatch {  portIn(R)  portIn(S)  portOut(Q)  portOut(nQ)  NOR(R, nQ, Q)  NOR(S, Q, nQ)}chip DLatch {  portIn(D)  portIn(EN)  portOut(Q)  portOut(nQ)  NOT(D, nD)  AND(D, EN, setD)  AND(nD, EN, rstD)  SRLatch(S=setD, R=rstD, Q=Q, nQ=nQ)}chip DFF {  portIn(D)  portIn(CLK)  portOut(Q)  portOut(nQ)  NOT(CLK, nCLK)  DLatch(D=D, EN=nCLK, Q=mid)  DLatch(D=mid, EN=CLK, Q=Q, nQ=nQ)}chip FA {  portIn(A)  portIn(B)  portIn(CI)  portOut(S)  portOut(CO)  XOR(A, B, p)  XOR(p, CI, S)  AND(A, B, g)  AND(p, CI, pc)  OR(g, pc, CO)}chip MUX2 {  portIn(A)  portIn(B)  portIn(S)  portOut(Y)  NOT(S, nS)  NAND(A, nS, na)  NAND(B, S, nb)  NAND(na, nb, Y)}chip AND3 {  portIn(A)  portIn(B)  portIn(C)  portOut(Y)  AND(A, B, ab)  AND(ab, C, Y)}chip OR3 {  portIn(A)  portIn(B)  portIn(C)  portOut(Y)  OR(A, B, ab)  OR(ab, C, Y)}chip OR4 {  portIn(A)  portIn(B)  portIn(C)  portIn(D)  portOut(Y)  OR(A, B, ab)  OR(C, D, cd)  OR(ab, cd, Y)}chip OR8 {  portIn(A)  portIn(B)  portIn(C)  portIn(D)  portIn(E)  portIn(F)  portIn(G)  portIn(H)  portOut(Y)  OR4(A=A, B=B, C=C, D=D, Y=lo)  OR4(A=E, B=F, C=G, D=H, Y=hi)  OR(lo, hi, Y)}chip DEC8 {  portIn(I0)  portIn(I1)  portIn(I2)  portOut(Y0)  portOut(Y1)  portOut(Y2)  portOut(Y3)  portOut(Y4)  portOut(Y5)  portOut(Y6)  portOut(Y7)  NOT(I0, n0)  NOT(I1, n1)  NOT(I2, n2)  AND3(A=n2, B=n1, C=n0, Y=Y0)  AND3(A=n2, B=n1, C=I0, Y=Y1)  AND3(A=n2, B=I1, C=n0, Y=Y2)  AND3(A=n2, B=I1, C=I0, Y=Y3)  AND3(A=I2, B=n1, C=n0, Y=Y4)  AND3(A=I2, B=n1, C=I0, Y=Y5)  AND3(A=I2, B=I1, C=n0, Y=Y6)  AND3(A=I2, B=I1, C=I0, Y=Y7)} power(VCC)ground(GND)clock(CLK)input(RST)NOT(RST, nR)button{label="1"}(AB0)button{label="2"}(AB1)button{label="3"}(AB2)button{label="4"}(AB3)button{label="5"}(AB4)button{label="6"}(AB5)button{label="7"}(AB6)button{label="8"}(AB7)button{label="Cancel"}(ACAN)NOR(p0, p1, atF)NOT(atF, natF)DEC8(I0=p2, I1=p3, I2=p4, Y0=y0, Y1=y1, Y2=y2, Y3=y3, Y4=y4, Y5=y5, Y6=y6, Y7=y7)OR3(A=t0, B=t1, C=t2, Y=OPEN)NOT(OPEN, ndoor)AND(y0, atF, AC0)AND(AC0, OPEN, O0)AND(y1, atF, AC1)AND(AC1, OPEN, O1)AND(y2, atF, AC2)AND(AC2, OPEN, O2)AND(y3, atF, AC3)AND(AC3, OPEN, O3)AND(y4, atF, AC4)AND(AC4, OPEN, O4)AND(y5, atF, AC5)AND(AC5, OPEN, O5)AND(y6, atF, AC6)AND(AC6, OPEN, O6)AND(y7, atF, AC7)AND(AC7, OPEN, O7)OR(ACAN, RST, kc)OR(O0, kc, kr0)NOT(kr0, nkr0)AND(AB0, nkr0, ks0)SRLatch(S=ks0, R=kr0, Q=AK0)OR(O1, kc, kr1)NOT(kr1, nkr1)AND(AB1, nkr1, ks1)SRLatch(S=ks1, R=kr1, Q=AK1)OR(O2, kc, kr2)NOT(kr2, nkr2)AND(AB2, nkr2, ks2)SRLatch(S=ks2, R=kr2, Q=AK2)OR(O3, kc, kr3)NOT(kr3, nkr3)AND(AB3, nkr3, ks3)SRLatch(S=ks3, R=kr3, Q=AK3)OR(O4, kc, kr4)NOT(kr4, nkr4)AND(AB4, nkr4, ks4)SRLatch(S=ks4, R=kr4, Q=AK4)OR(O5, kc, kr5)NOT(kr5, nkr5)AND(AB5, nkr5, ks5)SRLatch(S=ks5, R=kr5, Q=AK5)OR(O6, kc, kr6)NOT(kr6, nkr6)AND(AB6, nkr6, ks6)SRLatch(S=ks6, R=kr6, Q=AK6)OR(O7, kc, kr7)NOT(kr7, nkr7)AND(AB7, nkr7, ks7)SRLatch(S=ks7, R=kr7, Q=AK7)OR(y0, y1, a2)OR(a2, y2, a3)OR(a3, y3, a4)OR(a4, y4, a5)OR(a5, y5, a6)OR(a6, y6, a7)OR(y7, y6, b5)OR(b5, y5, b4)OR(b4, y4, b3)OR(b3, y3, b2)OR(b2, y2, b1)OR(b1, y1, b0)AND(AK1, y0, ru1)AND(AK2, a2, ru2)AND(AK3, a3, ru3)AND(AK4, a4, ru4)AND(AK5, a5, ru5)AND(AK6, a6, ru6)AND(AK7, a7, ru7)OR8(A=ru1, B=ru2, C=ru3, D=ru4, E=ru5, F=ru6, G=ru7, H=GND, Y=UPR)AND(AK0, b0, rd0)AND(AK1, b1, rd1)AND(AK2, b2, rd2)AND(AK3, b3, rd3)AND(AK4, b4, rd4)AND(AK5, b5, rd5)AND(AK6, y7, rd6)OR8(A=rd0, B=rd1, C=rd2, D=rd3, E=rd4, F=rd5, G=rd6, H=GND, Y=DNR)AND(AK0, y0, hk0)AND(AK1, y1, hk1)AND(AK2, y2, hk2)AND(AK3, y3, hk3)AND(AK4, y4, hk4)AND(AK5, y5, hk5)AND(AK6, y6, hk6)AND(AK7, y7, hk7)OR8(A=hk0, B=hk1, C=hk2, D=hk3, E=hk4, F=hk5, G=hk6, H=hk7, Y=hK)NOT(dir, ndir)NOT(UPR, nUPR)OR(ndir, nUPR, gOK)AND3(A=atF, B=ndoor, C=hK, Y=here)NOT(DNR, nDNR)OR(dir, nDNR, uOK)AND(UPR, uOK, mvUp)AND(DNR, gOK, mvDn)NOT(here, nhere)AND3(A=atF, B=ndoor, C=nhere, Y=decide)MUX2(A=dir, B=mvUp, S=decide, Y=dirN)AND(dirN, nR, dirD)DFF(D=dirD, CLK=CLK, Q=dir)OR(mvUp, mvDn, mv)AND(decide, mv, go1)OR(natF, go1, go)NOT(dirN, ndirN)AND(go, ndirN, dn)FA(A=p0, B=go, CI=GND, S=q0, CO=c0)FA(A=p1, B=dn, CI=c0, S=q1, CO=c1)FA(A=p2, B=dn, CI=c1, S=q2, CO=c2)FA(A=p3, B=dn, CI=c2, S=q3, CO=c3)FA(A=p4, B=dn, CI=c3, S=q4, CO=c4)AND(q0, nR, pd0)DFF(D=pd0, CLK=CLK, Q=p0)AND(q1, nR, pd1)DFF(D=pd1, CLK=CLK, Q=p1)AND(q2, nR, pd2)DFF(D=pd2, CLK=CLK, Q=p2)AND(q3, nR, pd3)DFF(D=pd3, CLK=CLK, Q=p3)AND(q4, nR, pd4)DFF(D=pd4, CLK=CLK, Q=p4)FA(A=t0, B=VCC, CI=GND, S=u0, CO=e0)FA(A=t1, B=VCC, CI=e0, S=u1, CO=e1)FA(A=t2, B=VCC, CI=e1, S=u2, CO=e2)AND(u0, OPEN, v0)AND(u1, OPEN, v1)AND(u2, OPEN, v2a)OR(v2a, here, v2)AND(v0, nR, td0)DFF(D=td0, CLK=CLK, Q=t0)AND(v1, nR, td1)DFF(D=td1, CLK=CLK, Q=t1)AND(v2, nR, td2)DFF(D=td2, CLK=CLK, Q=t2)OR8(A=AK0, B=AK1, C=AK2, D=AK3, E=AK4, F=AK5, G=AK6, H=AK7, Y=rAny)OR(rAny, natF, busy)AND(dir, busy, AUP)AND(ndir, busy, ADN)AND(AC0, ndoor, AD0)AND(AC1, ndoor, AD1)AND(AC2, ndoor, AD2)AND(AC3, ndoor, AD3)AND(AC4, ndoor, AD4)AND(AC5, ndoor, AD5)AND(AC6, ndoor, AD6)AND(AC7, ndoor, AD7)AND(y0, natF, AM0)AND(y1, natF, AM1)AND(y2, natF, AM2)AND(y3, natF, AM3)AND(y4, natF, AM4)AND(y5, natF, AM5)AND(y6, natF, AM6)OR8(A=y1, B=y2, C=y4, D=y5, E=y6, F=y7, G=GND, H=GND, Y=AFa)OR8(A=y0, B=y1, C=y2, D=y3, E=y6, F=y7, G=GND, H=GND, Y=AFb)OR8(A=y0, B=y2, C=y3, D=y4, E=y5, F=y6, G=y7, H=GND, Y=AFc)OR8(A=y1, B=y2, C=y4, D=y5, E=y7, F=GND, G=GND, H=GND, Y=AFd)OR3(A=y1, B=y5, C=y7, Y=AFe)OR4(A=y3, B=y4, C=y5, D=y7, Y=AFf)OR8(A=y1, B=y2, C=y3, D=y4, E=y5, F=y7, G=GND, H=GND, Y=AFg)speaker{mode="buzz", tone=880}(here)