Answer / carl_ellis

What is Foundation Fieldbus LAS?

Link Active Scheduler (LAS)
A Link Active Scheduler (LAS) is a deterministic,
centralized bus scheduler that maintains a list of
transmission times for all data buffers in all devices that
need to be cyclically transmitted. Only one Link Master
(LM) device on an H1 fieldbus Link can be functioning as
that link's LAS.

The Master and Primary Backup Link Active Scheduler (LAS)
shall reside in the host control system in redundant H1
network interface cards.

An additional backup LM Link Master (B/U LAS Link Active
Scheduler) shall be configured for all networks and shall
reside in the network device with the lowest field node
address. The Backup LAS should be placed in a separate
device that does not have controlling functions.

Primary and secondary interfaces should sit in separate
backplanes with separate CPUs, preferably in separate
control panels. Similarly, the primary and secondary power
supplies should not share the same backplane. Having
redundant interface cards, CPUs, and power supplies in the
same backplane is self-defeating since the backplane is a
single point of failure.

Each network shall be configured for automatic fail-over to
the Back-up LAS in the event of Master LAS failure.

Carl Ellis
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