Rockwell Automation 1794-L34 FlexLogix Controller System User Manual - Manual (Page 56)

Publication 1794-UM001G-EN-P - January 2007
56 Place, Configure, and Monitor I/O
When you add a module, you also define a specific configuration for
the module. While the configuration options vary from module to
module, there are some common options that you typically configure:
Configuration Option: Description:
requested packet interval (RPI) The RPI specifies the period at which data updates over a connection. For example, an
input module sends data to a controller at the RPI that you assign to the module.
• Typically, you configure an RPI in milliseconds (ms). The range is 0.2 ms
(200 microseconds) to 750 ms.
• If a ControlNet network connects the devices, the RPI reserves a slot in the stream of
data flowing across the ControlNet network. The timing of this slot may not coincide
with the exact value of the RPI, but the control system guarantees that the data
transfers at least as often as the RPI.
change of state (COS) Digital I/O modules use change of state (COS) to determine when to send data to the
controller. If a COS does not occur within the RPI timeframe, the module multicasts data at
the rate specified by the RPI.
Because the RPI and COS functions are asynchronous to the logic scan, it is possible for an
input to change state during program scan execution. If this is a concern, buffer input data
so your logic has a stable copy of data during its scan. Use the Synchronous Copy (CPS)
instruction to copy the input data from your input tags to another structure and use the
data from that structure.
communication format Many I/O modules support different formats. The communication format that you choose
also determines:
• data structure of tags
• connections
• network usage
• ownership
• whether the module returns diagnostic information
electronic keying When you configure a module, you specify the slot number for the module. However, it is
possible to place a different module in that slot, either on purpose or accidently. Electronic
keying lets you protect your system against the accidental placement of the wrong module
in a slot. The keying option you choose determines how closely any module in a slot must
match the configuration for that slot before the controller opens a connection to the
module. There are different keying options depending on your application needs.