Modbus Register Read — Drive Status

Briefing

A Modbus RTU comms card is mounted in the PLC rack and connected to the drive over RS-485. On every PLC scan the card reads the drive status register and maps three bits into BOOL inputs that your ladder can use directly: | Input | Meaning | |-------|---------| | **MB_RUNNING** | Drive output frequency > 0 (motor spinning) | | **MB_FAULTED** | Drive has an active fault code | | **MB_AT_SPEED** | Drive has reached the commanded speed reference | Your ladder task is straightforward — wire the panel and the feeder permissive: 1. **RUN_LAMP** mirrors MB_RUNNING. 2. **FAULT_LAMP** mirrors MB_FAULTED. 3. **SPEED_LAMP** mirrors MB_AT_SPEED. 4. **FEED_OK** — feeder permissive: MB_RUNNING AND NOT MB_FAULTED. Note: FEED_OK also serves as the drive RUN command. The physics engine uses it to start/stop the drive, closing the feedback loop.

Objectives

• RUN_LAMP := MB_RUNNING
• FAULT_LAMP := MB_FAULTED
• SPEED_LAMP := MB_AT_SPEED
• FEED_OK := MB_RUNNING AND NOT MB_FAULTED

I/O Table

Your program will be tested against:

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

1. #1Panel lamps mirror Modbus status bits

   Set each Modbus input individually and verify the matching lamp turns on.

2. #2FEED_OK = MB_RUNNING AND NOT MB_FAULTED

   FEED_OK on when running, off when faulted.

3. #3FEED_OK → physics drives MB_RUNNING (feedback loop)

   When FEED_OK=true the physics engine spins the drive; MB_RUNNING goes high and RUN_LAMP lights.