Yokogawa YVP110 - Manual (Page 130)

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IM 21B04C01-01E
Appendix 2. Link Master Functions
A2.1 Link Active Scheduler
A link active scheduler (LAS) is a deterministic, centralized bus scheduler that can control communications on
an H1 fieldbus segment. There is only one LAS on an H1 fieldbus segment.
A YVP supports the following LAS functions.
• PN transmission: Identifies a fieldbus device newly connected to the same fieldbus segment. PN is short
for Probe Node.
• PT transmission: Passes a token governing the right to transmit, to a fieldbus device on the same
segment. PT is short for Pass Token.
• CD transmission: Carry out a scheduled transmission to a fieldbus device on the same segment. CD is
short for Compel Data.
• Time synchronization: Periodically transmits the time data to all fieldbus devices on the segment and
returns the time data in response to a request from a device.
• Live list equalization: Sends the live list data to link masters on the same segment.
• LAS transfer: Transfers the right to be the LAS on the segment to another link master.
A2.2 Link Master
A link master (LM) is any device containing a link active scheduler. There must be at least one LM on a
segment. When the LAS on a segment has failed, another LM on the same segment starts working as the
LAS.
LM
Node address: 0x15
SlotTime = 5
LM
Node address: 0x16
SlotTime = 5
Node address: 0x14
SlotTime = 5
Basic device
Node address: 0xF1
Basic device
Node address: 0xF2
Basic device
Node address: 0xF3
Basic device
Node address: 0xF4
LAS
There are 3 LMs on this segment.
LM
FA0201.ai
Figure 1. Example of Fieldbus configuration-3 LMs on Same Segment
A2.3 Transfer of LAS
There are two procedures for an LM to become the LAS:
• If the LM whose value of [V(ST)×V(TN)] is the smallest on a segment, with the exception of the current
LAS, judges that there is no LAS on the segment, in such a case as when the segment has started up or
when the current LAS has failed, the LM declares itself as the LAS, then becomes the LAS. (With this
procedure, an LM backs up the LAS as shown in the following figure.)
• The LM whose value of [V(ST)×V(TN)] is the smallest on a segment, with the exception of the current LAS,
requests the LAS on the same segment to transfer the right of being the LAS, then becomes the LAS.
LM
Node address: 0x15
SlotTime = 5
LM
Node address: 0x16
SlotTime = 5
Node address: 0x14
SlotTime = 5
Basic device
Node address: 0xF1
Basic device
Node address: 0xF2
Basic device
Node address: 0xF3
Basic device
Node address: 0xF4
LAS
LAS
In the event that the current LAS in this segment
(node address 0x14) fails, the LM with the address
of 0x15 takes its place to become the LAS.
LM
FA0202.ai
Figure 2. Backup of LAS