Appendix 7. Link Master Functions; A7.1 Link Active Scheduler; A7.2 Link Master - YOKOGAWA digitalYEWFLO Series User Manual

APPENDIX 7. LINK MASTER FUNCTIONS

A7.1 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 digitalYEWFLO supports the following LAS functions.
1 PN transmission
2 PT transmission
3 CD transmission
4 Time synchronization
5 Live list equalization
6 LAS transfer

A7.2 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: 0x14
LAS
SlotTime = 5
LM LM
Node address: Node address:
0x15 0x16
SlotTime = 5 SlotTime = 5
Figure A7.1 Example of Fieldbus configuration-3 LMs on Same Segment
<APPENDIX 7. LINK MASTER FUNCTIONS>
Identifies a fieldbus device newly connected to the same fieldbus segment. PN is short for Probe
Node.
Passes a token governing the right to transmit, to a fieldbus device on the same segment. PT is
short for Pass Token.
Carry out a scheduled transmission to a fieldbus device on the same segment. CD is short for
Compel Data.
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.
Sends the live list data to link masters on the same segment.
Transfers the right to be the LAS on the segment to another link master.
Basic device Basic device
Node address: Node address:
0xF1 0xF2
There are 3 LMs on this segment.
Basic device Basic device
Node address: Node address:
0xF3 0xF4
A7-1
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