Check box and text box

++EDITED REPLY

You may be able to achieve that with a Mouse-Up event script executed from the checkbox.

For example, you can assign "030342" as the export value of the checkbox, so when the user ticks the checkbox the "CODIGO NC" text field populates that value; un-ticking the check box will clear that value.

You can try and see if something like this works for you:

var cb = event.target;

if (cb.value == "Off") {

this.getField("CODIGO NC").value  = "";

} else {

this.getField("CODIGO NC").value  = cb.value;

} 

Alternatively, the single line of code below may be a concise and more elegant script (in my opinion) which executes  the same results:

this.getField("CODIGO NC").value = (event.target.value == "Off") ? "" : cb.value;