CPE Profibus Network Architecture & Design 3 — Questions and Answers
Question 1: What is the purpose of the Profibus DP 'Freeze' command issued by a master to a group of slaves?
- Stops all network communication
- Freezes slave input data until a subsequent Freeze or Unfreeze command (Correct answer)
- Locks slave configuration parameters
- Prevents new slaves from joining the network
Correct answer: Freezes slave input data until a subsequent Freeze or Unfreeze command
The Freeze command causes a group of slaves to capture and hold their current input data until the master issues another Freeze or Unfreeze command.
Question 2: On a Profibus DP network operating at 1.5 Mbps, what is the maximum recommended cable segment length?
- 400 m (Correct answer)
- 200 m
- 100 m
- 50 m
Correct answer: 400 m
At 1.5 Mbps, the maximum recommended segment length for Profibus DP RS-485 cabling is 400 meters.
Question 3: Which Profibus DP diagnostic type is reported by a slave when a hardware fault is detected within the slave itself?
- Station diagnostics (Correct answer)
- Identifier-related diagnostics
- Channel-related diagnostics
- Extended diagnostics
Correct answer: Station diagnostics
Station diagnostics (Stat_Diag) are provided by the slave to report general hardware faults or conditions that apply to the entire slave station.
Question 4: In Profibus network design, what is the primary function of a bus terminator?
- Boosts signal strength for longer cable runs
- Prevents signal reflections at the cable ends (Correct answer)
- Converts RS-485 signals to fiber optic
- Provides galvanic isolation between segments
Correct answer: Prevents signal reflections at the cable ends
Bus terminators absorb the signal at each end of the Profibus cable segment to prevent reflections that could corrupt data transmission.
Question 5: What Profibus DP mechanism allows a master to synchronize the outputs of multiple slaves simultaneously?
- Freeze command
- Sync command (Correct answer)
- Global Control telegram
- Token passing
Correct answer: Sync command
The Sync command instructs a group of slaves to simultaneously apply their last received output data, enabling synchronized output updates across multiple slaves.
Question 6: Which address is reserved and cannot be assigned to any Profibus DP master or slave station?
- 0
- 126
- 127 (Correct answer)
- 255
Correct answer: 127
Address 127 is the global broadcast address in Profibus DP and cannot be assigned to any individual station.
Question 7: What is the key advantage of using Profibus PA over Profibus DP in process automation applications?
- Higher data throughput
- Intrinsic safety and power over the bus cable (Correct answer)
- Support for more stations per segment
- Faster baud rates up to 12 Mbps
Correct answer: Intrinsic safety and power over the bus cable
Profibus PA uses IEC 61158-2 physical layer technology that provides intrinsic safety and delivers power to field devices over the same two-wire bus cable.
CPE Profibus Network Architecture & Design 3
What is the purpose of the Profibus DP 'Freeze' command issued by a master to a group of slaves?