Rockwell Automation 1756-IF4FXOF2F ControlLogix High-speed Analog I/O Module - Manual (Page 103)

Rockwell Automation Publication 1756-UM005B-EN-P - January 2013 103
Data Storage Appendix A
If you choose the Archiving Connection communication format, you receive up
to 20 analog samples per update, but you receive only one CST timestamp per
module update. With an archiving connection, the CST timestamp is associated
with the .LastUpdateIndex sample. In a typical case, the LastUpdateIndex value is
equal to 19, .Input[19] is the newest sample, and the timestamp is associated with
sample Input[19]. The other samples are older than the current timestamp by
approximately 1 RTS time per sample.
EXAMPLE If .LastUpdateIndex = 6, then the CST Timestamp is associated with .Input[6],
and .Input[6] is the newest sample followed by the subsequent samples in the
order below.
.Input[5] is approximately 1 RTS older than the current CST Timestamp.
.Input[4] is approximately 2 RTSs older than the current CST Timestamp.
.Input[3] is approximately 3 RTSs older than the current CST Timestamp.
…
.Input[0] is approximately 6 RTSs older than the current CST Timestamp.
.Input[19] is approximately 7 RTSs older than the current CST Timestamp.
.Input[18] is approximately 8 RTSs older than the current CST Timestamp.
…
.Input[7] is approximately 19 RTSs older than the current CST Timestamp.
In this example, .Input[7] is the oldest sample provided.