BenchChapter 10: Meshes

B79INTERLOCK

The task

P0 asks the hoist to go up, P1 asks it to go down. P2 drives up, P3 drives down.

A request is granted only while the other direction is off; it then holds until released.

A request that waited is granted as soon as the other side lets go.

The board

The chip's ports, each with its kind and the parts its signal reaches. Cyan reads, lemon writes. On a narrow screen, scroll the board sideways to see all of it.

Sources: V1 5 V, V2 5 V square at 20 Hz, V3 5 V, and V4 5 V square at 12.5 Hz
Resistors: R1 330 Ω and R2 330 Ω
LEDs: D1 green and D2 red
Probes: CH1, CH2, CH3, and CH4

Key idea

Never drive both: while one output is on, ignore the other request.

Hints

Each hint goes a step further than the one before. Open them one at a time.

Hint 1Show

When nothing is on, check both requests and grant the first you find.

Hint 2Show

Write a loop for each direction that holds until its request drops.

Solution

Reveal the Full SolutionThe complete program for INTERLOCK. Open it only when you want the answer.

The reference program

The game's own solution. It passes every test and scores exactly par on every benchmark.

One direction at a time; each holds until released.

u1SC-2 standard

I: IN P0
JNZ U
IN P1
JZ I
OUT P3
DN: IN P1
JNZ DN
OUT P3
JMP I
U: OUT P2
W: IN P0
JNZ W
OUT P2

CYCLES: 1800; at par
ENERGY: 3600; at par
NODES: 1; at par
INSTRUCTIONS: 13; at par