PLC Communication and Handshake
Exchange safe test bits/registers with a PLC simulator and implement request/acknowledge sequencing.
Learning objective
Exchange safe test bits/registers with a PLC simulator and implement request/acknowledge sequencing.
Components and tools
- Development board
- Current-limited low-voltage supply
- Digital multimeter
- Oscilloscope or logic analyser
- Emergency power disconnect
Safety before motion
- Never connect student code directly to a production PLC.nUse network segmentation and read-only access first.nSafety functions belong in safety-rated hardware/logic.
Practical procedure
- Create a PLC simulator project.nDefine command, acknowledgement, busy and fault tags.nConnect using a test protocol/driver.nIssue one command and wait for matching acknowledgement.nTest timeout, duplicate and fault states.
Measurement checkpoints
| Checkpoint | Expected | Instrument | Safety limit |
|---|---|---|---|
| Handshake | Command/ack sequence completes once | PLC watch table | Timeout enforcednFault |
Troubleshooting
| Symptom | Check | Corrective action |
|---|---|---|
| No response | Check addressing/protocol/route | Verify simulator connectionnRepeats action |
Engineering sizing tools
Calculate before powering
Mandatory pre-start gate
Machine safety checklist
The simulated enable button remains locked until every item is confirmed.