CPE Communication Protocols & Standards 5 — Questions and Answers
Question 1: What distinguishes PROFIBUS FMS from PROFIBUS DP in terms of application use case?
- FMS targets cell-level peer-to-peer communication with complex data objects; DP targets fast I/O at field level (Correct answer)
- FMS operates at 12 Mbps only; DP operates at lower speeds
- FMS is wireless; DP uses wired RS-485
- FMS uses token bus; DP uses polling only
Correct answer: FMS targets cell-level peer-to-peer communication with complex data objects; DP targets fast I/O at field level
PROFIBUS FMS (Fieldbus Message Specification) was designed for supervisory-level communication with complex data models, while DP is optimized for fast cyclic I/O with field devices.
Question 2: Which IEC 61784 profile family specifically covers PROFIBUS communication profiles?
- CP 3/x (Communication Profile Family 3) (Correct answer)
- CP 1/x
- CP 2/x
- CP 6/x
Correct answer: CP 3/x (Communication Profile Family 3)
IEC 61784 Communication Profile Family 3 (CPF 3) defines the PROFIBUS DP and PA communication profiles.
Question 3: In PROFIBUS DP, what happens when two masters have the same station address configured?
- Both masters will fail to join the logical token ring, causing bus disruption (Correct answer)
- The lower-priority master automatically changes its address
- One master becomes a passive standby
- The conflict is resolved by the GSD file manager
Correct answer: Both masters will fail to join the logical token ring, causing bus disruption
Duplicate master addresses cause token ring initialization failures and can disrupt all communication on the bus segment.
Question 4: What is the data transfer rate used by PROFIBUS PA on its MBP physical layer?
- 31.25 kbps (Correct answer)
- 9.6 kbps
- 1.5 Mbps
- 93.75 kbps
Correct answer: 31.25 kbps
PROFIBUS PA operates at a fixed 31.25 kbps on the Manchester-coded, bus-powered (MBP) physical layer.
Question 5: Which PROFIBUS extension standard addresses functional safety up to SIL 3?
- PROFIsafe (Correct answer)
- PROFIdrive
- PA Profile
- DP-V2 isochronous
Correct answer: PROFIsafe
PROFIsafe is the PROFIBUS (and PROFINET) safety communication profile certified for use in applications requiring up to SIL 3 per IEC 61508.
Question 6: When using a PROFIBUS repeater, which parameter is critical to configure correctly to avoid bus timing errors?
- The Tslot (slot time) and minimum station delay (Tsdl) to account for repeater propagation delay (Correct answer)
- The slave watchdog timer only
- The GSD file baud rate entry
- The token holding time (Tth)
Correct answer: The Tslot (slot time) and minimum station delay (Tsdl) to account for repeater propagation delay
Repeaters add propagation delay, so Tslot and station delay parameters in the bus parameter set must be increased to ensure correct timing across all segments.
Question 7: What is the correct wire color convention for PROFIBUS cable according to EN 50170?
- Green wire = A line (negative/N), Red wire = B line (positive/P) (Correct answer)
- Red wire = A line, Blue wire = B line
- Yellow wire = A line, Green wire = B line
- Blue wire = A line, Red wire = B line
Correct answer: Green wire = A line (negative/N), Red wire = B line (positive/P)
EN 50170 specifies green for the A line (RxD/TxD-N) and red for the B line (RxD/TxD-P) in standard PROFIBUS cable.
CPE Communication Protocols & Standards 5
What distinguishes PROFIBUS FMS from PROFIBUS DP in terms of application use case?