CPE Communication Protocols & Standards 4 — Questions and Answers
Question 1: What is the purpose of the Slave Diagnostic Data in PROFIBUS DP?
- Reports module-level faults, configuration errors, and device-specific status to the master (Correct answer)
- Stores historical trend data for process variables
- Broadcasts alarm messages to all network nodes
- Reconfigures slave I/O mapping remotely
Correct answer: Reports module-level faults, configuration errors, and device-specific status to the master
PROFIBUS DP slave diagnostic data provides structured fault information including station, module, and channel-level diagnostics to the Class 1 master.
Question 2: Which profile defines how PROFIBUS devices communicate in process automation applications involving transmitters and positioners?
- PA Profile 3.02 (Correct answer)
- PROFIsafe
- PROFIdrive
- PROFIenergy
Correct answer: PA Profile 3.02
The PA Profile (currently version 3.02) standardizes device descriptions and data formats for process automation instruments on PROFIBUS PA.
Question 3: In the PROFIBUS protocol stack, which layer handles data sequencing and segmentation?
- PROFIBUS uses only Layers 1, 2, and 7; Layers 3-6 are not used (Correct answer)
- Layer 3 (Network Layer)
- Layer 4 (Transport Layer)
- Layer 5 (Session Layer)
Correct answer: PROFIBUS uses only Layers 1, 2, and 7; Layers 3-6 are not used
PROFIBUS implements only the Physical (Layer 1), Data Link (Layer 2), and Application (Layer 7) layers of the OSI model, omitting Layers 3–6.
Question 4: What is the function of the Sync command in PROFIBUS DP?
- Forces slaves to hold their output values until a new Sync or Unsync command (Correct answer)
- Synchronizes the master clock to UTC time
- Aligns slave firmware versions across a segment
- Sets all slave addresses to sequential values
Correct answer: Forces slaves to hold their output values until a new Sync or Unsync command
The Sync command instructs a group of slaves to freeze their current output states, ignoring new output data until Unsync is issued.
Question 5: Which mechanism does PROFIBUS DP use to detect a lost slave device?
- Watchdog timer on the slave that resets outputs if no valid message is received within a configured time (Correct answer)
- Heartbeat broadcasts from master every 100 ms
- ARP-style address resolution probes
- Redundant media switchover detection
Correct answer: Watchdog timer on the slave that resets outputs if no valid message is received within a configured time
PROFIBUS DP slaves have a configurable watchdog timer that triggers a safe-state output condition if no valid cyclic data frame is received within the timeout period.
Question 6: What is the maximum number of PROFIBUS segments that can be connected using repeaters in a single network?
- Up to 9 segments (with up to 4 repeaters in series per path) (Correct answer)
- Up to 32 segments
- Up to 5 segments
- Unlimited segments with managed switches
Correct answer: Up to 9 segments (with up to 4 repeaters in series per path)
PROFIBUS allows up to 9 segments by cascading repeaters, but each signal path may have no more than 4 repeaters in series to maintain signal integrity.
Question 7: How is the PROFIBUS DP bus address assigned to a new slave device?
- Via DIP switches, an MMI on the device, or using a Class 2 master tool (Correct answer)
- Automatically via DHCP-like protocol from the master
- By physical position on the bus segment
- By the GSD file during network startup
Correct answer: Via DIP switches, an MMI on the device, or using a Class 2 master tool
PROFIBUS DP slave addresses are set manually through hardware (DIP switches), a local display/keypad, or remotely using a Class 2 master programming tool.
CPE Communication Protocols & Standards 4
What is the purpose of the Slave Diagnostic Data in PROFIBUS DP?