I don’t understand the first question. But the following may help.
In the second part, you wrote: “This is why I am struggling to understand the recent revision. According to it, the input term is generated by Avyakata PS. But I don’t understand how can one do stuff like walk down the stair (purana kamma) by only mano sankhara. .”
- Paticca Samuppada should not be used to describe things like walking down the stairs to the bathroom or actions like that.
- It is focused on kamma accumulation, mainly to generate kammic energy to bring about future rebirths in various realms. That is why it is “akusala-mula PS.”
The other point that could be helpful is the following:
- Each citta in a citta vithi with a specific symbol engages in a specific task.
- The presence of the seven javana cittas in a citta vithi means that the mind is engaged with that sensory input and generates kammic energy with raga, dosa, or moha.
- The presence of two tadarammana citta (T) at the end of the javanas indicates that the mind has “locked into” the sensory input. “Tadarammana” is translated as “registration,” meaning the mind has shifted from the “uppatti bhvanaga state” to take a new mindset. For example, upon hearing the news of the death of a close relative, the mind shifts to a “saddened state.” Then that mindset becomes a “temporary bhvanaga state” that could replace the “uppatti bhvanaga state” for hours or even days.
- See “Bhava and Bhavaṅga – Simply Explained!” and “State of Mind in the Absence of Citta Vithi – Bhavaṅga.”
- More references are in the new post, “Mūlapariyāya Sutta – The Root of All Things.”