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Entry type: FAQ Entry ID: 58836417, Entry date: 02/12/2016

How do you access the "Running" bit of timers in STEP 7 (TIA Portal)?

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With STEP 7 (TIA Portal) V11 and higher it is no longer possible to access the "Running" bit of a timer in an instance data block. Below we describe how you can access this bit or simulate it.

With migrated projects the "RU" tag ("Running" bit) is partially accessed from a single instance of a timer. This is no longer permitted in STEP 7 (TIA Portal) V11 and higher. The tag is marked red in the TIA Portal and the following error message occurs when compiling:
"Accessing private and internal tags is not permitted."

This FAQ response describes a special case when using timers.
In normal utilization the appropriate timer is started and the output Q is used. This also secures the timer behavior. The "Running" bit visible in the instance only indicates that the timer is running. This is necessary to implement the selected timer behavior as on/off delay (TON/TOF).
If only a running timer is required in the application, the output Q of the pulse timer (TP) should be used.

Fig. 1

Remedy 1
  1. Do not create a new single instance, but create a multi-instance.
  2. Access the "Running" bit ("RU") locally. (Example: #instTimer.RU)

    Fig. 2

Remedy 2
Using the interconnection of the other Boolean tags of the timer instance data block you can simulate the "RU" "Running" bit as below, depending on the type of timer:
Timer Interconnection
TP With the "Generate pulse" timer TP the "Running" bit (instance DB tag "RU") corresponds to the output signal of the timer (instance DB tag "Q").

With the TON "ON delay" and TONR "Latching ON delay" timers, the "Running" bit (instance DB tag "RU") results from a link between the input signal (instance DB tag "IN") as NO (normally open) contact and the output signal (instance DB tag "Q") as NC (normally closed) contact.

Fig. 3

TOF With the TOF "OFF delay" timer, the "Running" bit results from a link between the input signal (instance DB tag "IN") as NC contact and the output signal (instance DB tag "Q") as NO contact.

Fig. 4

Table 1

Creation Environment
The screens in this FAQ response were created with STEP 7 (TIA Portal) V13.

Always use the combination from the instance data block tags (and not a buffering of them), because in the case of asynchronous querying the buffer does not necessarily reflect the current state.

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