Private Sub поле1_Change()
Call adhLimitChars(поле1, N)
Me.Поле2.Requery
End Sub

Option Compare Database
Option Explicit

 ' From Access 2002 Desktop Developer's Handbook 
 ' by Litwin, Getz, and Gunderloy. (Sybex) 
 ' Copyright 2001.  All rights reserved. 

Private Declare Function SendMessageLong _
 Lib "user32" Alias "SendMessageA" _
 (ByVal hWnd As Long, ByVal wMsg As Long, _
 ByVal wParam As Long, lngValue As Long) As Long

Private Declare Function GetFocus _
 Lib "user32" () As Long

Private Const EM_SETLIMITTEXT As Long = &HC5

Public Sub adhLimitChars(txt As TextBox, lngLimit As Long)
 
    Dim hWnd As Long
    Dim lngResult As Long
    Dim lngNewMax As Long

    hWnd = GetFocus()

    lngNewMax = Len(txt.Text)
    Forms![Form].Поле2 = lngNewMax
    If lngNewMax < lngLimit Then
        lngNewMax = lngLimit
    End If
    SendMessageLong hWnd, EM_SETLIMITTEXT, lngNewMax,  0 
End Sub