Rockwell Automation 1756-IF4FXOF2F ControlLogix High-speed Analog I/O Module - Manual (Page 102)

102 Rockwell Automation Publication 1756-UM005B-EN-P - January 2013
Appendix A Data Storage
Remote Module Considerations
If the 1756-IF4FXOF2F module is not in the same chassis as its
owner-controller, the following considerations apply:
• Update rates can be slower for network interface cards and network
bandwidth, especially with faster RTS rates, such as less than 4 ms.
• If the remote module is on a ControlNet network, the modules still
retrieves channel input data at the RTS rate, but the module produces data
on the network only at the RPI rate.
• If the remote module is on the EtherNet/IP network, the module still
retrieves channel input data at the RTS rate, but the module produces data
on the network at a rate no faster than the RPI divided by four.
Choose a
Communication Format To determine which communication format to use for your data storage
application, consider these factors:
• Whether your application requires a CST timestamp
A CST timestamp is useful in these scenarios:
–
You need to know when data samples are retrieved.
– Your application has other modules or axis data that provide a CST
timestamp and your application needs to establish a time relationship
between the analog data and the other modules or axis.
• The rate at which your application needs to produce data samples
The combination of RTS and RPI values determines the rate at which new
data is produced, as described in
Timing Relationships on page 101 .
Table 14 - Communication Formats
CST Timestamp
Required Data Sample Rate Recommended
Communication Format Description
Yes Faster than 4 ms Archiving Connection Returns up to 20 floating-point, archived data samples for each channel. Returns a single CST and rolling
timestamp.
The module stores individual samples on-board until it retrieves the final sample. The module then
produces all samples in one packet.
Yes 4 ms or slower
(1)
CST Timestamped Float Data Returns one floating-point data sample for each channel. Returns CST and rolling timestamps.
No Float Data Returns one floating-point data sample for each channel. Returns a rolling timestamp, but not a CST
timestamp.
(1) This recommendation is based on balancing speed and controller resources. In some applications, a rate faster than 4 ms can be possible.