Rockwell Automation Allen-Bradley 1769-IF4, Руководство пользователя

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Publication 1769-UM002B-EN-P - July 2005
4-4 Module Data, Status, and Channel Configuration for the Output Modules
1769-OF2 Output Data Loopback/Echo
Words 2 and 3 provide output loopback/data echo through the input array for
channels 0 and 1, respectively. The value of the data echo is the analog value
currently being converted on-board the module by the D/A converter. This
ensures that the logic-directed state of the output is true. Otherwise, the state
of the output could vary depending on controller mode.
Under normal operating conditions, the data echo value is the same value that
is being sent from the controller to the output module. Under abnormal
conditions, the values may differ. For example:
1. During run mode, the control program could direct the module to a
value over or under the defined full range. In that case, the module
raises the over- or under-range flag and continues to convert and data
echo up to the defined full range. However, upon reaching either the
maximum upper or lower full range value, the module stops converting
and echoes back that maximum upper or lower full range value, not the
value being sent from the controller.
2. During program or fault mode with Hold Last State or User-Defined
Value selected, the module echoes the hold last value or alternate value
you selected. For more information on the hold last and user-defined
values, see 1769-OF2 Fault Value (Channel 0 and 1) on page 4-11 and
1769-OF2 Program/Idle Value (Channel 0 and 1) on page 4-11.