[AccessD] textbox value is null

I am trying to use the value of a text box I am typing into to create a string in another text box. 
  IOW I type 'a' in txt1 and txt2 is set to 'C:\Access\a\'.  The C:\Access is a constant directory 
location and I am inserting 'C:\Access\' & txtA.Value & '\' into txtB.

However txtA.Value is NULL! until I move out of the text box (after update) so the string I am 
building looks like 'C:\Access\\' since a null is being inserted between the 'C:\Access\' and the 
'\'.  I thought I was going to use txtA.OnKeyDown etc.  No dice.  I never really knew about this 
behavior and don't quite know how to work around it.

Any thoughts?

-- 
John W. Colby
Colby Consulting

Reality is what refuses to go away
when you do not believe in it