Instruction Manual

APPENDIX 1. LINK MASTER FUNCTIONS 5-1
IM 12A00A01-61E
APPENDIX 1. LINK MASTER FUNCTIONS
A1-1 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 EXA202 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.
A1-2 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
Figure A1-1. Example of Fieldbus configuration-3 LMs on Same Segment