Mixing : Automation : Writing Automation to the Start, End, or All of a Track or Selection : Requirements for Standard Write Automation Commands

Requirements for Standard Write Automation Commands
For automation data to be written for a specific parameter, the associated track must be in one of the following Automation modes and meet the following conditions:
Latch Mode
The control for the parameter must be changed (touched) during the automation pass.
Touch Mode
The control for the parameter must be changed (touched).
Write Mode
All controls on that track must be in Write mode.
This command can be undone.
To write current automation values to the start, end, or all of a track or Edit selection:
1 Choose Window > Automation.
2 Make sure that the automation type is write-enabled.
3 Do one of the following:
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– or – 
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4 Start playback.
5 Make sure you are actively writing on the appropriate track if you are in Latch or Touch mode.
6 When you reach a point in the track or selection that contains the automation data you want to apply, click the Write Automation to Start, All, or End button in the Automation window.
7 Stop playback.
The current values of all write-enabled automation at that point are written to the corresponding area of the track/selection.