Calling subroutine in dynamic actions

Hi experts

Whenever the infotype value for employee first name changes (P0001-VORNR) then I want to call my subroutine VALIDATE_ENTRY in Program ZCHECK.

I am using dynamic action entry as follows : 06 1 F VALIDATE_ENTRY(ZCHECK)

In my ABAP Program VALIDATE_ENTRY how would I determine what the value of my screen variables are, I need to know what the Employee Number is and also what the modified value of P0001-VORNR is.

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