Rockwell Automation 1769-IF4XOF2 Compact 8-Bit Low Resolution Analog I/O Combination Module - Manual (Page 15)

Publication 1769-UM008A-EN-P - November 2001
Overview 1-5
System Operation
At power-up, the module performs a check of its internal circuits,
memory, and basic functions. During this time, the module status LED
remains off. If no faults are found during power-up diagnostics, the
module status LED is turned on.
After power-up checks are complete, the module waits for valid
channel configuration data. If an invalid configuration is detected, the
module generates a configuration error. Once a channel is properly
configured and enabled, it begins the analog-to-digital or
digital-to-analog conversion process.
Input Channels
Each time an input channel is read by the module, that analog data
value is tested by the module for an over-range condition (e.g. input
voltage greater than 10V dc). If such a condition is detected, a unique
bit is set in the channel status word. The channel status word is
described in Input Data File on page 4-3.
The controller reads the analog data from the module. This typically
occurs at the end of the program scan or when commanded by the
control program. If the controller and the module determine that the
bus data transfer was made without error, the data is used in your
control program.
Output Channels
The module monitors output channels for over-range conditions. If
such a condition is detected, a unique bit is set in the channel status
word. The channel status word is described in Output Data File on
page 4-7.
The module receives proportional binary values from the bus master
(e.g. controller). This typically occurs at the end of the program scan
or when commanded by the control program. If the controller and the
module determine that the bus transfer was completed without error,
the module converts the data to an analog output signal.