CPE Profibus Network Architecture & Design 4 — Questions and Answers
Question 1: What is the function of a DP/PA coupler or link in a Profibus network architecture?
- Converts RS-485 signals to Ethernet
- Connects a Profibus DP segment to a Profibus PA segment (Correct answer)
- Bridges two DP segments of different baud rates
- Converts Profibus to HART protocol
Correct answer: Connects a Profibus DP segment to a Profibus PA segment
A DP/PA coupler or link connects a high-speed Profibus DP segment to a lower-speed Profibus PA segment, adapting both the physical layer and baud rate.
Question 2: In Profibus DP, which token-passing mechanism determines which master currently has the right to communicate with slaves?
- CSMA/CD
- Token ring logical bus (Correct answer)
- Master-slave polling only
- Time Division Multiple Access (TDMA)
Correct answer: Token ring logical bus
Profibus uses a logical token ring among masters on a physical bus; the master holding the token has exclusive rights to initiate communication with slaves.
Question 3: Which Profibus DP data exchange mode supports acyclic read/write services in addition to cyclic I/O?
- DP-V0
- DP-V1 (Correct answer)
- DP-V2
- DP-PA
Correct answer: DP-V1
Profibus DP-V1 extended the original DP-V0 specification to include acyclic read/write services for parameter access, alarms, and extended diagnostics.
Question 4: When designing a Profibus DP network, which factor most directly determines the maximum permissible baud rate?
- Number of slave stations
- Total cable length of the longest segment (Correct answer)
- Number of masters on the network
- Watchdog timer setting
Correct answer: Total cable length of the longest segment
The maximum baud rate is limited by the total cable segment length, since longer cables have higher capacitance and attenuation that restrict signal frequency.
Question 5: In a Profibus DP-V2 isochronous mode, what is the primary benefit over standard DP-V0 operation?
- Greater number of supported slaves
- Deterministic, equidistant bus cycle for motion control applications (Correct answer)
- Automatic baud rate negotiation
- Wireless extension of the network
Correct answer: Deterministic, equidistant bus cycle for motion control applications
DP-V2 isochronous mode provides a strictly equidistant (deterministic) bus cycle time, which is essential for precision motion control applications requiring synchronized drives.
Question 6: What is the correct pin assignment for the Profibus RS-485 signal 'RxD/TxD-P (B)' on a standard 9-pin Sub-D connector?
- Pin 3 (Correct answer)
- Pin 5
- Pin 6
- Pin 8
Correct answer: Pin 3
On the standard Profibus 9-pin Sub-D connector, RxD/TxD-P (the positive data line, also called B-line) is assigned to pin 3.
Question 7: Which Profibus DP slave parameter in the GSD file specifies the number of bytes the slave sends to the master per cycle?
- Max_Input_Len (Correct answer)
- Data_Control_Time
- Freeze_Mode_supp
- Ident_Number
Correct answer: Max_Input_Len
Max_Input_Len in the GSD file defines the maximum number of input bytes (data from slave to master) that the slave device can send per communication cycle.
CPE Profibus Network Architecture & Design 4
What is the function of a DP/PA coupler or link in a Profibus network architecture?