Rockwell Automation 1769-OF2 Compact I/O Analog Modules - Manual (Page 103)

Publication 1769-UM002B-EN-P - July 2005
Module Data, Status, and Channel Configuration for the Output Modules 4-21
1769-OF8C and -OF8V Output Held Bits (H0 through H7)
Word 1, bits 2, 6, 10, and 14, and Word 2, bits 2, 6, 10, and 14 contain the
output held bits for input channels 0 through 7. When one of these bits is set
(1), the corresponding channel is in the hold state. Output data will not change
until value commanded by the controller matches the value being held by the
module for any held output channel.
When the value commanded for a channel by the controller matches the value
being held by the module, the Output Held bit for that channel is cleared (0).
The output channel can again be directly controlled by the values commanded
in the Output Data file by the controller. The control can determine the
output value being held by the module for any channel whose Output Held bit
is set (1) by reading words 3 to 10 of the Input Data file.
1769-OF8C and -OF8V Output Data Loopback/Echo
Words 3 through 10 provide output loopback/data echo through the input
array for channels 0 through 7. 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-OF8C and -OF8V Fault Value on page 4-31 and
1769-OF8C and -OF8V Program/Idle Value on page 4-32.
3. When one or more of the output channel’s Output Held bits are set (1).
See 1769-OF8C and -OF8V Output Held Bits (H0 through H7) on
page 4-21.