diff --git a/fhem/FHEM/44_S7.pm b/fhem/FHEM/44_S7.pm
index 0e863c165..edd619a27 100644
--- a/fhem/FHEM/44_S7.pm
+++ b/fhem/FHEM/44_S7.pm
@@ -320,7 +320,7 @@ sub S7_Attr(@) {
 
 				Log3( $name, 3, "$name S7_Attr: setting MaxReadLength= $aVal" );
 			}
-		} elsif ($aName eq "MaxMessageLength") {
+		} elsif ($aName eq "Intervall") {
 			if ( $aVal >= 1 ) {
 
 				$hash->{Interval} = $aVal;
diff --git a/fhem/FHEM/44_S7_S5Client.pm b/fhem/FHEM/44_S7_S5Client.pm
index c06eab2d5..107965a4a 100644
--- a/fhem/FHEM/44_S7_S5Client.pm
+++ b/fhem/FHEM/44_S7_S5Client.pm
@@ -56,6 +56,7 @@ sub new {
 	$self->{__davet121003} = [ 0x12, &DLE, &ETX ];
 	
 	$self->{PDULength} = &MaxPduSize;
+	$self->{MaxReadLength} = ($self->{PDULength} - 18);
 		
 
 	#my @__davet1006 = ( &DLE, &ACK );
@@ -837,4 +838,4 @@ sub S5WriteS5Bytes($$$$$$) {
 
 =end html_DE
 
-=cut
\ No newline at end of file
+=cut