diff --git a/jtag/ChangeLog b/jtag/ChangeLog
index d3cb74a6..bbed2c9e 100644
--- a/jtag/ChangeLog
+++ b/jtag/ChangeLog
@@ -1,3 +1,7 @@
+2008-12-23  Arnim Laeuger  <arniml@users.sourceforge.net>
+
+   * src/svf/svf.c: added debug output for svf_compare_tdo()
+
 2008-12-23  Kolja Waschk <kawk>
 
    * src/tap/parport/direct.c, configure.ac, doc/UrJTAG.txt:
diff --git a/jtag/src/svf/svf.c b/jtag/src/svf/svf.c
index 61b68d15..ef2f0377 100644
--- a/jtag/src/svf/svf.c
+++ b/jtag/src/svf/svf.c
@@ -54,6 +54,11 @@
 #include "fclock.h"
 #endif
 
+
+/* define for debug messages */
+#undef DEBUG
+
+
 int svfparse(parser_priv_t *priv_data, chain_t *chain);
 
 
@@ -449,6 +454,13 @@ svf_compare_tdo(parser_priv_t *priv, char *tdo, char *mask, tap_register *reg, Y
               loc->last_line+1, 
               loc->last_column+1 );
     }
+
+#ifdef DEBUG
+    printf( "Expected : %s\n", tdo_bit );
+    printf( "Mask     : %s\n", mask_bit );
+    printf( "TDO data : %s\n", reg->string );
+#endif
+
     if (priv->svf_stop_on_mismatch)
       result = 0;
   }