Beginner 10 — Count to five (CTU)

Briefing

A photo-eye watches boxes drop into a carton. Pulse BOX_EYE once per box. After five boxes the carton is full and the CARTON_FULL lamp turns on. Tap CNT_RESET to clear the count so the next carton starts from zero. That is the whole job: no motor and no START button yet. A CTU ("Count Up") is a counter block, added from More instructions just like the TON timer. BOX_EYE feeds its count input (CU), CNT_RESET feeds its reset input (R), its preset (PV) is 5, and its Q (done) output turns on when the count reaches 5. The CTU counts each false-to-true change at CU by itself, so BOX_EYE connects straight in.

Objectives

• Fewer than five BOX_EYE pulses → CARTON_FULL stays off
• The fifth BOX_EYE pulse → CARTON_FULL turns on
• Tap CNT_RESET → count clears, CARTON_FULL off, the next five boxes fill a new carton

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #1Five BOX_EYE pulses → CARTON_FULL on

   Five rising edges on BOX_EYE bring the CTU to its preset, so Q lights the lamp

2. #2Four BOX_EYE pulses → CARTON_FULL still off

   One short of the preset: the counter is not done, so the lamp stays off

3. #3CNT_RESET after a full carton → lamp off, next carton counts from zero

   Reset clears the counter: four more boxes keep the lamp off and the fifth lights it again