User manual

Publication 1768-UM001C-EN-P - November 2007
Configure and Monitor I/O 57
Configuration Options for I/O Modules
Configuration Option Description
Requested Packet Interval (RPI)
(applies to local 1769 I/O and
distributed I/O)
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 minimum RPI for 1769 I/O is 1 millisecond.
• 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)
(only applies to distributed I/O)
Digital I/O modules use COS to determine when to send data to the controller. If a COS does not occur
within the RPI time frame, the module multicasts data at the specified 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
(only applies to distributed I/O)
Many I/O modules support different formats. The chosen communication format also determines:
• data structure of tags.
• connections.
• network use.
• ownership.
• whether the module returns diagnostic information.
Electronic Keying
(applies to local 1769 I/O and
distributed I/O)
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. Electronic keying lets you protect your system against the
accidental placement of the wrong module in a slot. The chosen keying option determines how closely
any module in a slot must match the configuration for that slot before the controller will open a
connection to the module. Keying options differ depending on your application needs.
IMPORTANT
The RSLogix 5000 configuration dialogs for 1769 I/O modules
offer a Hold Last State option for how to react when the
controller faults.
Although the 1768-L43 an 1768-L45 controllers do not support
the Hold Last State option for 1769 I/O modules when they are
configured locally, this feature is available when they are
connected on DeviceNet using a 1769-ADN adapter.