BenchChapter 11: Capstones

B85SIGMA DELTA

The task

P0 reads a knob on CH1. P1 is a plain digital pin; R1 and C1 average it onto CH2.

On each tick of P2, add half the reading to B. At 50 or more, take 50 off and drive P1 high.

Otherwise drive P1 low. CH2 settles at the knob's level.

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 3.5 V, V2 2 V square at 12.5 Hz, and V3 1 V square at 6.25 Hz
Resistors: R1 22 kΩ
Capacitors: C1 1 µF
Probes: CH1 and CH2

Key idea

Half the reading is at most 50, so B stays under 100 and fits in a word.

Hints

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

Hint 1Show

A reading of 30 adds 15 a tick, so P1 is high on 3 ticks out of 10.

Hint 2Show

SUB 50 and JL decide; on the low path, ADD 50 back before you store B.

Solution

Reveal the Full SolutionThe complete program for SIGMA DELTA. 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.

A first order sigma delta modulator.

u1SC-2 standard

L: IN P2
IN P0
DIV 2
ADD B
SUB 50
JL Z
MOV B, A
MOV A, 1
OUT P1
JMP L
Z: ADD 50
MOV B, A
MOV A, 0
OUT P1

CYCLES: 791; at par
ENERGY: 1582; at par
NODES: 1; at par
INSTRUCTIONS: 14; at par