BenchChapter 6: Trees

B39PRESCALER

The task

V1 drives P0 with a fast square wave. Divide it by six for the LED on P1:

count the rising edges, and keep the LED lit for counts 3, 4, and 5 of every six.

Counts 0, 1, and 2 leave it dark. The first edge is count 1.

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 square at 250 Hz
Resistors: R1 330 Ω
LEDs: D1 green
Probes: CH1 and CH2

Key idea

A rising edge is a 1 read after a 0: wait out the high, then wait for the next one.

Hints

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

Hint 1Show

Keep the count in B. MOD 6 brings it back to 0 after 5.

Hint 2Show

DIV 3 turns counts 0 to 2 into 0 and counts 3 to 5 into 1.

Solution

Reveal the Full SolutionThe complete program for PRESCALER. 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.

The LED runs at one sixth of the input.

u1SC-2 standard

L: IN P0
JNZ L
H: IN P0
JZ H
MOV A, B
ADD 1
MOD 6
MOV B, A
DIV 3
OUT P1

CYCLES: 720; at par
ENERGY: 1440; at par
NODES: 1; at par
INSTRUCTIONS: 10; at par