BSD-340-user-guide-eng, Doc. 1004474-2, 2020-09-18,
Autronica Fire and Security AS
Page 9
2. Traffic like alarms or analogue values received by another loop
➢ Wrong detector reported.
➢ Traffic in one loop could ruin traffic in another loop, this would cause excessive
retransmissions which in turn could disturb other loops.
2.4.2 Crosstalk countermeasures
The BSD-340 software has some countermeasures to handle crosstalk.
Note! The wiring of the loops (see chapter 2.4) are very important to follow to minimize the
occurrence of crosstalk.
1. Loop ID
Each PowerLoop includes a “loop ID” in every restart message. The BSD-340 can then
ignore restarts from other loops. The “loop ID” is normally the BSD-340’s address on the
AutroFieldBus.
Note! There must be a way to accept wrong IDs so that new detectors and moved
detectors can be accepted.
2. Checksum seeded with LoopID
All PowerLoop messages have a 16-bit CRC (checksum) so that the receiver can ignore
messages ruined by noise. Each loop calculates CRC differently by seeding the CRC
algorithm with the LoopID. This means that all units on a PowerLoop can ignore messages
from other loops, even if they are influenced by crosstalk. The BSD-340 can also
determine what loop a crosstalk message comes from.
3. Timeslots
A PowerLoop unit always listens to the loop and avoids transmitting if someone else is
transmitting, but if two starts simultaneously there will be a collission, and both stop
sending. This problem, due to collisions, is solved by a “timeslot” system, and starting
transmission in a random timeslot. This strategy increases the chance to get a message
through.
Note! Crosstalk messages will reduce capacity from neighbour loops.
4. Slow retransmissions
The BSD-340 SW version 1.1.0, or later, no longer has a time delay in retransmissions of
messages, which was used for avoiding mutual jamming. The high number of timeslots
available for retransmissions makes a better use of bandwidth and assures that messages
get through.
5. Fault message “crosstalk”
When crosstalk is detected the BSD-340 will report a fault message to the AutroSafe
panel. This can be used during commissioning to reduce crosstalk.
6. Crosstalk “mode” of BSD-340
There is a “crosstalk mode” in the BSD-340. This is done by setting the address switches to
+40 (see chapter 5.4.1).
• No crosstalk fault messages (as they would become very annoying in systems with
continuous crosstalk)
• Ignore RESTART messages from other loops
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