Rockwell Automation 1756-XXXX ControlLogix Analog I/O Modules - Manual (Page 24)

24 Publication 1756-UM009C-EN-P - December 2010
Chapter 2 Analog I/O Operation in the ControlLogix System
Input Module Operation In traditional I/O systems, controllers poll input modules to obtain their input
status. In the ControlLogix system, a controller does not poll analog input
modules after a connection is established. Instead, the modules multicast their
data periodically. The frequency depends on the options chosen during
configuration and where in the control system that input module physically
resides.
An input module’s behavior varies depending upon whether it operates in the
local chassis or in a remote chassis. The following sections detail the
differences in data transfers between these set-ups.
Input Modules in
a Local Chassis When a module resides in the same chassis as the owner-controller, the
following two configuration parameters will affect how and when an input
module produces data:
• Real Time Sample (RTS)
• Requested Packet Interval (RPI)
Real Time Sample (RTS)
This configurable parameter, which is set during the initial configuration by
using RSLogix5000 software, instructs the module to perform two
basic operations:
1. Scan all of its input channels and store the data into on-board memory.
2. Multicast the updated channel data (as well as other status data) to the
backplane of the local chassis.
On-Board Memory
Status Data
Channel Data
Channel Data
Channel Data
Channel Data
Channel Data
Channel Data
Ch 0
Ch 1
Ch 2
Ch 3
Ch 4
Ch 5
Timestamp
41361
1
2