Rockwell Automation PLC-5 Fieldbus Solutions for Integrated Architecture User Manual - Manual (Page 69)

Publication 1757-UM006A-EN-P - May 2002
Integrating Fieldbus into Rockwell Automation Logix System 2-25
Link Schedule
The Link Schedule is the overall schedule for the link. It includes both
the link data transfer and the device function block execution
schedules. An independent Link Schedule is provided for the FIM
interface port for each link. A backup Link Schedule is provided for all
Link Master capable devices on the link.
The link data transfer schedule is derived from the portion of the link
schedule that deals with publication of parameters. The Control
Builder (CB) provides a default link schedule of publications and
function block execution phasing based on the function block
connections in the user configured control strategy. The basis for the
link schedule is this link's content from all currently loaded Control
Modules (CM). Execution phasing is based solely on function block
existence in the CM. Order of execution is based on the order in CM
(ORDERINCM) parameter for each block. Publications are based on
inter-device function block connections and device to ProcessLogix or
ProcessLogix to device function block connections. The following
publication rules apply.
• Function block publications appear in the link data transfer
schedule in the order specified by their ORDERINCM
parameters. (Duplicate values of ORDERINCM may produce
indeterminate ordering of those blocks involved.)
• If the user changes the sequence of execution order for function
blocks in a schedule, the ORDERINCM parameters of the
involved function blocks are appropriately adjusted.
• Publication of each output is scheduled immediately after
execution of the function block that produces the value,
considering inter-publication delays and potential conflicts.
• Blocks publish, if their output is connected to an input in
another device or the FIM.
• No unneeded time delay is allowed in the default link data
transfer schedule.
• The macrocycle is the least common multiple of the execution
periods of all the CMs involved in the link data transfer
schedule.