BenchChapter 5: Half duplex

B29SCHMITT

The task

P0 reads a slow sine wave with a fast ripple on top.

One threshold would flicker as the ripple crosses it, so use two:

turn the LED on P1 on at 3.5 volts, and off only once the input falls to 1.5 volts.

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 0.5 V square at 500 Hz, V2 2 V sine at 25 Hz, and V3 2.5 V
Resistors: R1 330 Ω
LEDs: D1 yellow
Probes: CH1 and CH2

Key idea

3.5 and 1.5 volts read as 70 and 30 percent.

Hints

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

Hint 1Show

Two waiting loops: one waits for the reading to reach 70, the other for it to drop to 30.

Hint 2Show

Between the loops, switch the LED. JL and JG keep each loop going.

Solution

Reveal the Full SolutionThe complete program for SCHMITT. 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.

On at 3.5 volts, off at 1.5 volts.

u1SC-2 standard

L: IN P0
SUB 70
JL L
MOV A, 1
OUT P1
H: IN P0
SUB 30
JG H
MOV A, 0
OUT P1

CYCLES: 800; at par
ENERGY: 1600; at par
NODES: 1; at par
INSTRUCTIONS: 10; at par