Siemens S7-200 System Manual page 114

Operating Your Text Display (TD) Device
5.5 Viewing the Screens and the Alarms
The operator can edit or accept variable values by pressing the ENTER key. The TD device
will write the updated variable value to the CPU and set the edit notification bit for that
variable when the operator presses the ENTER key. The TD device then moves the cursor
to the next editable variable. Pressing ENTER for the last editable variable of an alarm writes
this last value to the S7-200 CPU and the TD device then resets the alarm enable bit. For
more information on editing variables, see Editing a Variable that is Embedded in an Alarm
or a Screen in Chapter 5.
Every alarm falls into one of four possible alarm acknowledgement and editing types. This
section explains specifically how each alarm type is handled by the TD device. The four
alarm types follow:
● No acknowledgement required. No edits allowed
● Acknowledgement required. No edits allowed
● No acknowledgement required. Edits allowed
● Acknowledgement required. Edits allowed
No Acknowledgement Required, No Edits Allowed
In this combination of no acknowledgement required and no edits allowed, the TD device
simply displays the alarm. The ENTER key has no function since there are no editable
variables within the alarm. The alarm may contain variables that are updated at the update
rate of the TD device. This type of alarm is replaced on the display if a higher priority alarm is
enabled by the S7-200 CPU. The operator can either press the UP or the DOWN arrow key
to scroll to other alarms or press ESC to return to the menus.
The TD device does not clear the corresponding alarm-enable bit in the S7-200 CPU.
Acknowledgement Required, No Edits Allowed
In this combination of acknowledgement required and no edits allowed, the TD device
displays the alarm and makes the entire alarm flash (blink) until the operator presses ENTER
to acknowledge the alarm. Variable values are updated from the S7-200 CPU at the normal
update rate while the alarm is flashing.
When the operator presses ENTER, the TD device:
● Sets the acknowledgement-notification bit for this alarm.
● Clears the alarm-enable bit for this alarm. This causes the alarm to be removed from the
Another alarm cannot replace the one flashing until the operator acknowledges the flashing
alarm. This is also true even if a higher priority alarm is enabled in the S7-200 CPU. If the TD
device is configured for single line alarms and the CPU enables a higher priority alarm, the
flashing alarm shifts down to the next line of the display. The operator cannot press the UP
or the DOWN key to scroll through other enabled alarms until the current alarm is
acknowledged.
No Acknowledgement Required, Edits Allowed
In this combination of no acknowledgement required and edits allowed, the TD device
displays a alarm and then waits for the operator to edit a value in the alarm. All of the
variables within the alarm are updated at the update rate. Since the alarm does not require
acknowledgement, this type of alarm is removed from the TD device display if a higher
priority alarm is enabled in the S7-200 CPU.
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display on the next update cycle.
Text Display (TD) User Manual
System Manual, 08/2008, A5E00765548-03