User`s guide

On-line Monitoring and Diagnostics
Forcing an Output
210 UMC800 Control Builder User’s Guide Release E
1/01
Forcing an Output
Overview
The ability to force the output [pin] of function blocks and variables from the Control Builder is provided
as an aid to startup and configuration troubleshooting. The feature is limited to single output per block. The
majority of blocks have a single output, and most of the multiple output blocks have an obvious primary
(i.e. most important) output. This may apply to the block’s primary analog output (such as for an AI block)
or digital output of a logic block (such as for a DI or DO block). Some blocks (i.e. Loop Blocks) do not
have a forcible output. It is not possible to force function block outputs from the Operator Interface.
Variables, which are normally set to 0 on download of a new configuration or a change in configuration can
have their output value changed on-line. You can also preset value of a variable using an initialization
procedure via function blocks. Refer to Appendix D – Controller Initialization which shows the use of a
recipe block or write variable block for this purpose.
You can also display a list of blocks that are presently being forced.
All forced outputs are cleared by a CONTROLLER COLD START.
CAUTION
During Live-Monitoring (especially fast logic), it is possible to see transient states where the
block output is inconsistent with its input values. This occurs because it is possible for the
input values and outputs values to be taken from different controller execution cycles.
Therefore either the viewed inputs or outputs may be "older".
Solution: Recognize this possibility when interpreting results. Use forcing if necessary to
create and assess static conditions.
Forcing an output
Follow the procedure in Figure 66 to force an output.
1. Select OUT
in the dialog
box.
2. Enter the
output value in
the entry field.
3. Click “WRITE”.
The output value will
change to the value
entered for forcing.
.
4. To remove forcing, click
on “ Remove Force”. The
original selection for the
parameter will return.
.
Figure 66 Force an output