diff --git a/libraries/base/diag/src/vhdl/diag_pkg.vhd b/libraries/base/diag/src/vhdl/diag_pkg.vhd
index d81881785e4c23e6eeceef3abfd78a7535a9c103..8e3c0eb5e50914ed7a5090ba1d3c5c19fd2dc169 100644
--- a/libraries/base/diag/src/vhdl/diag_pkg.vhd
+++ b/libraries/base/diag/src/vhdl/diag_pkg.vhd
@@ -102,9 +102,10 @@ PACKAGE diag_pkg IS
   -----------------------------------------------------------------------------
   
   -- control register
-  CONSTANT c_diag_bg_reg_nof_dat : NATURAL := 8;
-  CONSTANT c_diag_bg_reg_adr_w   : NATURAL := ceil_log2(c_diag_bg_reg_nof_dat);
-  
+  CONSTANT c_diag_bg_reg_nof_dat  : NATURAL := 8;
+  CONSTANT c_diag_bg_reg_adr_w    : NATURAL := ceil_log2(c_diag_bg_reg_nof_dat);
+  CONSTANT c_diag_bg_reg_adr_span : NATURAL := 2**c_diag_bg_reg_adr_w;
+
   CONSTANT c_diag_bg_mode_w               : NATURAL :=  8;
   CONSTANT c_diag_bg_samples_per_packet_w : NATURAL := 24;   
   CONSTANT c_diag_bg_blocks_per_sync_w    : NATURAL := 24;