CPE CPE Network Topology & Cabling Standards 1 — Questions and Answers
Question 1: What is the maximum segment length for PROFIBUS DP operating at 1.5 Mbit/s using Type A cable?
- 100 m
- 200 m
- 400 m (Correct answer)
- 1000 m
Correct answer: 400 m
At 1.5 Mbit/s, PROFIBUS DP Type A cable supports a maximum segment length of 400 meters before a repeater is required.
Question 2: Which cable type is the recommended standard cable for PROFIBUS DP installations per IEC 61158?
- Type A — shielded twisted pair, 135–165 Ω impedance (Correct answer)
- Type B — unshielded twisted pair, 100 Ω impedance
- Type C — multi-drop coaxial cable
- Type D — fiber optic duplex cable
Correct answer: Type A — shielded twisted pair, 135–165 Ω impedance
Type A cable (shielded twisted pair with 135–165 Ω characteristic impedance, ≤30 pF/m capacitance) is the IEC 61158 standard recommendation for PROFIBUS DP.
Question 3: How many repeaters can be cascaded in a PROFIBUS DP network, and what is the resulting maximum network span at 93.75 kbit/s?
- 3 repeaters, 3,000 m
- 9 repeaters, 10,000 m (Correct answer)
- 9 repeaters, 9,600 m
- 15 repeaters, 15,000 m
Correct answer: 9 repeaters, 10,000 m
Up to 9 repeaters can be cascaded, and at 93.75 kbit/s (segment length 1,200 m) the total network span can reach approximately 10,000 meters.
Question 4: What is the maximum number of stations (nodes) per PROFIBUS DP segment including the master?
- 16
- 32 (Correct answer)
- 64
- 126
Correct answer: 32
Each PROFIBUS DP segment supports a maximum of 32 stations (addresses 0–31), including masters and slaves.
Question 5: In a PROFIBUS DP network, what is the function of bus termination resistors and where must they be placed?
- They filter EMI and are placed on every node
- They match cable impedance to prevent signal reflections and must be placed at both ends of each segment (Correct answer)
- They limit current and are placed only at the master
- They provide pull-up voltage and are placed at any convenient location
Correct answer: They match cable impedance to prevent signal reflections and must be placed at both ends of each segment
Termination resistors match the cable's characteristic impedance to absorb signal energy at each segment end, preventing reflections that cause communication errors.
Question 6: What is the correct pin assignment for the PROFIBUS DP signal lines on a standard 9-pin D-Sub connector?
- Pin 3 = RxD/TxD-P (B line), Pin 8 = RxD/TxD-N (A line) (Correct answer)
- Pin 2 = RxD/TxD-P (B line), Pin 7 = RxD/TxD-N (A line)
- Pin 4 = RxD/TxD-P (B line), Pin 6 = RxD/TxD-N (A line)
- Pin 1 = RxD/TxD-P (B line), Pin 9 = RxD/TxD-N (A line)
Correct answer: Pin 3 = RxD/TxD-P (B line), Pin 8 = RxD/TxD-N (A line)
Per the PROFIBUS standard, Pin 3 carries RxD/TxD-P (the positive/B signal line) and Pin 8 carries RxD/TxD-N (the negative/A signal line) on a 9-pin D-Sub connector.
CPE CPE Network Topology & Cabling Standards 1
What is the maximum segment length for PROFIBUS DP operating at 1.5 Mbit/s using Type A cable?