A Link Master device controls when devices access the fieldbus and executes the link schedule which synchronizes communications with function block execution on the fieldbus.
The H1 card or any field device that supports Link Master functionality can function as a Link Master device.
Only one Link Master device can be active at a time on the fieldbus segment. This device is called the LAS.
The DeltaV system can configure one Link Master device to function as the primary Link Master device.
When the primary Link Master device is attached to the fieldbus, it takes over as the LAS.
The H1 card always functions as the primary Link Master.
When the H1 card is redundant, the secondary H1 functions as the primary Link Master if the primary H1 card fails.
All other Link Master devices are backup Link Master devices that can take over as LAS only if the primary Link Master device fails.
One backup Link Master field device is supported per fieldbus segment. The fieldbus devices communicate on a schedule (executed by the LAS) as required to implement the control strategy.