CPE Profibus Network Architecture & Design 5 — Questions and Answers
Question 1: What is the maximum total number of stations supported across an entire Profibus DP network (using repeaters)?
- 32
- 64
- 126 (Correct answer)
- 246
Correct answer: 126
Profibus DP supports a maximum of 126 stations across the entire network (addresses 0–125), regardless of the number of segments or repeaters used.
Question 2: In a Profibus network with multiple masters, how is bus access arbitrated between Class 1 masters?
- Priority queuing based on station address
- Token passing in ascending address order (Correct answer)
- CSMA/CA collision avoidance
- Time-slotted access controlled by a bus coordinator
Correct answer: Token passing in ascending address order
Multiple Profibus masters share the bus using a logical token ring where the token is passed in ascending station address order, granting each master a turn to communicate.
Question 3: Which Profibus DP feature allows a slave to notify the master of an alarm or event without waiting to be polled?
- DP-V0 cyclic interrupt
- DP-V1 alarm acknowledgment mechanism (Correct answer)
- DP-V2 publisher/subscriber
- Global Freeze command
Correct answer: DP-V1 alarm acknowledgment mechanism
DP-V1 introduced an alarm mechanism where slaves can signal alarms to the master, and the master must explicitly acknowledge receipt of each alarm.
Question 4: When installing Profibus RS-485 cable near high-voltage power cables, what minimum separation distance is generally recommended?
- 5 cm
- 20 cm (Correct answer)
- 50 cm
- 100 cm
Correct answer: 20 cm
A minimum separation of 20 cm (200 mm) between Profibus cables and high-voltage power cables is generally recommended to reduce electromagnetic interference.
Question 5: What is the purpose of the 'Ident_Number' field in a Profibus GSD file?
- Specifies the slave's bus address
- Uniquely identifies the slave device type to the master (Correct answer)
- Defines the maximum input data length
- Sets the watchdog timer value
Correct answer: Uniquely identifies the slave device type to the master
The Ident_Number is a unique 2-byte identifier assigned by the Profibus organization that identifies the specific device type, allowing masters to verify correct device configuration.
Question 6: In Profibus DP-V2, the 'publisher/subscriber' model enables which advanced communication capability?
- Slaves communicating directly with other slaves (cross-communication) (Correct answer)
- Masters broadcasting configuration to all slaves simultaneously
- Automatic baud rate detection by new devices
- Redundant master takeover without data loss
Correct answer: Slaves communicating directly with other slaves (cross-communication)
DP-V2 publisher/subscriber (also called slave-to-slave communication or Data Exchange Broadcast) allows slave devices to directly exchange data with other slaves without master intervention.
Question 7: Which optical fiber interface standard is commonly used to extend Profibus DP networks in environments with severe electromagnetic interference?
- 10BASE-FL
- OLM (Optical Link Module) with BFOC/2.5 connectors (Correct answer)
- SFP transceiver with LC connectors
- POF (Plastic Optical Fiber) with RJ45 adapters
Correct answer: OLM (Optical Link Module) with BFOC/2.5 connectors
Profibus OLMs (Optical Link Modules) using BFOC/2.5 (ST-style) connectors are the standard solution for fiber optic extension of Profibus DP networks in high-EMI environments.
CPE Profibus Network Architecture & Design 5
What is the maximum total number of stations supported across an entire Profibus DP network (using repeaters)?