Rockwell Automation 1769-OF4VI Compact I/O Isolated Analog Modules - Manual (Page 13)

Publication 1769-UM014B-EN-P - May 2010
Overview 1-5
System Operation
When you cycle power, the module performs a check of its internal circuits,
memory, and basic functions. During this time, the module status OK LED
remains off. If no faults are found during power-cycle diagnostics, the module
status OK LED is turned on.
After power-cycle 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 Modules
Each time a channel is read by the input module, that analog data value is
tested by the module for an over-range or under-range condition. If any of
these conditions are detected, unique bits are set in the channel status word.
The channel status word is described in the 1769-IF4I Input Data File on
page 3-3.
The controller reads the two’s complement binary converted analog data from
the modules. This typically occurs at the end of the program scan or when
commanded by the control program. If the controller and the modules
determine that the bus data transfer was made without error, the data is used
in your control program.
Output Modules
The output modules monitor channels for over-range and under-range
conditions and can also clamp the outputs at designated levels (if enabled by
the user program). If such conditions are detected, a unique bit is set in the
channel status word.
The channel status word is described in the 1769-OF4CI and -OF4VI Output
Data File on page 4-3.
The output modules receive two’s complement binary values from the bus
master. 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 output
module converts the data to an analog output signal.