diff --git a/library/interface.dcm b/library/interface.dcm
index 67238d74..a4f1179b 100644
--- a/library/interface.dcm
+++ b/library/interface.dcm
@@ -154,6 +154,12 @@ K Ethernet PHY MII RMII 10/100Mpbs
 F http://www.ti.com/lit/ds/symlink/dp83848c.pdf
 $ENDCMP
 #
+$CMP DS89C21
+D Differential CMOS Line Driver and Receiver Pair, SOIC-8
+K rs422 tranciever
+F http://www.ti.com/lit/ds/symlink/ds89c21.pdf
+$ENDCMP
+#
 $CMP EL7242C
 D Translateur TTL->VMOS. Double driver VMOS
 $ENDCMP