How get the value of a field type select.

Hi, i have a form with a field type SELECT. it field has in General Settings: Disabled field to : INSERT/UPDATEMODE.
When i try from a button get the value of it field, SC shows the value Empty.:
Script for the button:
echo "The value is: ".{ESTADO};

BUT, If i change in General Settings: Disabled field to : NO.
The value is returned correctly.

My question is how can i get the value when this button is disabled?

[ATTACH=CONFIG]n67359[/ATTACH]
This is the fields’s configuracion.

field_disabled.PNG