diff --git a/z21emu/z21emu.cc b/z21emu/z21emu.cc
index e9ddefd..b850bda 100644
--- a/z21emu/z21emu.cc
+++ b/z21emu/z21emu.cc
@@ -18,6 +18,7 @@ void i2cloop(I2C *i2c);
 void i2cscan(I2C *i2c);
 void i2ccfgprint();
 int i2ccfgload(const char *fname);
+int debug = 0;
 void help();
 
 
@@ -40,6 +41,10 @@ int main (int argc, char **argv) {
 			i2ccfgprint();
 			exit (0);
 		}
+		
+		if (strcmp (argv[i], "-debug") == 0) {
+			debug = 1;
+		}
 
 		if (strcmp (argv[i], "-config") == 0) {
 			i++;
@@ -85,8 +90,13 @@ void i2cloop (I2C *i2c) {
 	// digital in
 	for (index = 0; index < RBUS_MAXSENSORBYTES; index++) {
 		if (rbus[index].i2c_addr != 0) {
-			if (!i2c->ReadByte(rbus[index].i2c_addr, rbus[index].i2c_reg, &rbus[index].status))
+			if (!i2c->ReadByte(rbus[index].i2c_addr, rbus[index].i2c_reg, &rbus[index].status)) {
+				if (debug) printf ("i2cloop: Read ADDR:%02x REG:%02x Value:%2x Error\n", rbus[index].i2c_addr, rbus[index].i2c_reg, rbus[index].status);
 				rbus[index].status = 0xFF;		// error
+			}
+			else if (debug) {
+				printf ("i2cloop: Read ADDR:%02x REG:%02x Value:%2x\n", rbus[index].i2c_addr, rbus[index].i2c_reg, rbus[index].status);
+			}
 		}
 	}
 
@@ -268,6 +278,7 @@ void help () {
 	printf ("parameters: without any parameters the config will be read from file.\n");
 	printf ("            if no file is found, autoscan is used first.\n");
 	printf ("   -scan           scanning i2c bus and print out a sample device config\n");
+	printf ("   -debug          enabling debugging\n");
 	printf ("   -config FILE    finename used for configuration (default %s/\n", DEFAULT_CONFIG);
 	printf ("\n");
 }
diff --git a/z21emu/z21emu.h b/z21emu/z21emu.h
index dea348f..7abecfb 100644
--- a/z21emu/z21emu.h
+++ b/z21emu/z21emu.h
@@ -44,7 +44,7 @@ struct s_xlanturnout {
 };
 
 extern struct s_xlanturnout xlturn[XLAN_TURNOUT_MAX];
-
+extern int debug;
 
 void xlan_turnout (int addr, bool enable);