--- 3m-810.pl	2008/10/03 21:25:02	20
+++ 3m-810.pl	2008/10/03 21:47:24	21
@@ -70,6 +70,9 @@
 
 =cut
 
+my $tags_data;
+my $visible_tags;
+
 my $port=new Device::SerialPort($device) || die "can't open serial port $device: $!\n";
 warn "using $device $handshake $baudrate $databits $parity $stopbits" if $debug;
 $handshake=$port->handshake($handshake);
@@ -125,20 +128,24 @@
 			warn "## tags ",as_hex($tags), " [$tl] = ",dump( $tags ) if $debug;
 			print "seen $nr tags: ", join(',', @tags ) , "\n";
 
-			# read data from tag
-			read_tag( $_ ) foreach @tags;
+			my $removed_tags = $visible_tags;
+			$visible_tags = {};
+
+			foreach my $tag ( @tags ) {
+				next if $visible_tags->{$tag}++;
+				read_tag( $tag );
+				if ( delete $removed_tags->{$tag} ) {
+					print "removed tag $tag\n";
+				}
+			}
 
 		}
 	}
 ) foreach ( 1 .. 100 );
 
-my $read_cached;
-
 sub read_tag {
 	my ( $tag ) = @_;
 
-	return if $read_cached->{ $tag }++;
-	
 	print "read_tag $tag\n";
 
 	cmd(
@@ -163,8 +170,8 @@
 				warn sprintf "## tag %08s %02d %s |%-4s|\n", $tag, $ord, as_hex( $data ), $data;
 				$data[ $ord ] = $data;
 			}
-			$read_cached->{ $tag } = join('', @data);
-			print "DATA $tag ",dump( $read_cached ), "\n";
+			$tags_data->{ $tag } = join('', @data);
+			print "DATA $tag ",dump( $tags_data ), "\n";
 		}
 	);