CPE Communication Protocols & Standards 3 — Questions and Answers
Question 1: What is the purpose of the 'Freeze' command in PROFIBUS DP?
- Synchronizes input data capture across multiple slaves simultaneously (Correct answer)
- Halts all bus communication for maintenance
- Locks the token to a single master
- Freezes the slave watchdog timer
Correct answer: Synchronizes input data capture across multiple slaves simultaneously
The Freeze command causes a group of slaves to simultaneously latch their input data until a new Freeze or Unfreeze command is issued.
Question 2: Which baud rate is NOT supported by PROFIBUS DP?
- 125 kbps (Correct answer)
- 9.6 kbps
- 12 Mbps
- 500 kbps
Correct answer: 125 kbps
PROFIBUS DP supports 9.6 kbps through 12 Mbps but does not include 125 kbps as a standard baud rate option.
Question 3: What is the maximum number of nodes (including masters and slaves) on a single PROFIBUS segment without repeaters?
- 32 (Correct answer)
- 64
- 126
- 256
Correct answer: 32
A single PROFIBUS segment can have up to 32 nodes; repeaters are required to extend beyond this limit.
Question 4: In PROFIBUS DP-V2, what feature enables isochronous operation for motion control?
- Time-synchronized cyclic data exchange with defined jitter (Correct answer)
- Redundant token ring failover
- HART multiplexing over PROFIBUS
- ODVA-compatible device profiles
Correct answer: Time-synchronized cyclic data exchange with defined jitter
DP-V2 isochronous mode provides deterministic, time-synchronized data exchange with sub-millisecond jitter for coordinated motion control.
Question 5: Which connector type is specified as standard for PROFIBUS DP field connections?
- 9-pin D-sub (DB9) (Correct answer)
- RJ45
- M12 circular connector
- BNC coaxial
Correct answer: 9-pin D-sub (DB9)
The 9-pin D-sub (DB9) connector is the standard PROFIBUS connector defined in the EN 50170 specification for field devices.
Question 6: What is the role of the bus terminator resistor network in PROFIBUS DP?
- Prevents signal reflections at cable ends by matching line impedance (Correct answer)
- Provides power to bus-powered devices
- Filters EMI noise from the data lines
- Sets the baud rate for the segment
Correct answer: Prevents signal reflections at cable ends by matching line impedance
Termination resistors at both ends of a PROFIBUS segment match the cable's characteristic impedance (typically 150 Ω) to prevent signal reflections.
Question 7: How does PROFIBUS PA differ from PROFIBUS DP in terms of physical layer power delivery?
- PA delivers power to field devices over the same two-wire bus used for communication (Correct answer)
- PA uses a separate power cable alongside the data cable
- PA requires 24 VDC on a dedicated power rail
- PA uses wireless power delivery to field devices
Correct answer: PA delivers power to field devices over the same two-wire bus used for communication
PROFIBUS PA uses the MBP physical layer to deliver both communication signals and power to field devices on the same two-wire bus.
CPE Communication Protocols & Standards 3
What is the purpose of the 'Freeze' command in PROFIBUS DP?