Honeywell Series 8 I/O - I;O Link Performance Specifications; Reviewing Link Unit Utilization; Table 6 Link Unit Utilization Rates

2. Series 8 I/O Planning and Design
2.7. I/O Link performance specifications
36 Series 8 I/O User's Guide R500
Honeywell April 2017
2.7 I/O Link performance specifications
The transmission rate of data on an IOLINK configured with Series 8 I/O is 2000 Link
Units per second where a Link Unit is defined as being approximately equivalent to one
parameter read (or write) per second.
TIP
If your configuration exceeds 2000 LUs on a Series 8 I/O IOLINK, then an I/O
Link Access Overrun can occur. This type of overrun occurs when parameter
reads and writes are not completed within their cycle time. This indicates too
many parameter access requests were attempted through the I/O Link.
The IOLINK function block generates a "439, IOLINK Process Data collection
Overrun" alarm when an I/O Link overrun occurs.
Reviewing Link Unit utilization
The Link Unit utilization cycle rate varies depending on the type of block being used.
The following table defines the specifications for the various blocks.
Table 6 Link Unit utilization rates
Block names
Data processing
Link Units per
cycle time
Cycle time
Every primary IOM
Event Collection
1
500 ms
Every secondary IOM
Event Collection
1
500 ms
Digital Input-xxx IOM
blocks
PV Scanning
1.75
IOM block's
SCANRATE
Digital Output-xxx IOM
blocks
BACKCALC Scanning
1.25
IOM block's
SCANRATE
Analog Input-xxx IOM
blocks
PV Scanning
5
IOM block's
SCANRATE
Analog Output-xxx IOM
blocks
BACKCALC Scanning
5
IOM block's
SCANRATE
AOCHANNEL
OP Store
1
OP connector's CM
Execution Rate
status output for
DOCHANNEL
SO Store
1
SO connector's CM
Execution Rate