diff --git a/xschem_library/logic/mux21.sch b/xschem_library/logic/mux21.sch
new file mode 100644
index 00000000..be7cf9ba
--- /dev/null
+++ b/xschem_library/logic/mux21.sch
@@ -0,0 +1,54 @@
+v {xschem version=3.4.6RC file_version=1.2
+*
+* This file is part of XSCHEM,
+* a schematic capture and Spice/Vhdl/Verilog netlisting tool for circuit
+* simulation.
+* Copyright (C) 1998-2023 Stefan Frederik Schippers
+*
+* This program is free software; you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation; either version 2 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program; if not, write to the Free Software
+* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+}
+G {
+
+a: process( G , D, RST )
+begin
+if( RST = '1') then
+  Q <= '0' after delay ;
+  QN <= '1' after delay ;
+elsif ( G = '1' ) then
+  Q <= D after delay ;
+  QN <= not D after delay ;
+end if ;
+end process ;
+
+ }
+K {}
+V {
+assign #del Z = S ? B : A; 
+}
+S {}
+E {}
+C {opin.sym} 280 -320 0 0 {name=p5 lab=Z}
+C {ipin.sym} 120 -320 0 0 {name=p2 lab=S}
+C {use.sym} 70 -720 0 0 {------------------------------------------------
+library ieee;
+        use ieee.std_logic_1164.all;
+        use ieee.numeric_std.all;}
+C {ipin.sym} 120 -440 0 0 {name=p14 lab=A}
+C {title.sym} 160 -30 0 0 {name=l17}
+C {ipin.sym} 120 -380 0 0 {name=p3 lab=B}
+C {noconn.sym} 280 -320 2 1 {name=l4}
+C {noconn.sym} 120 -440 2 0 {name=l2}
+C {noconn.sym} 120 -380 2 0 {name=l3}
+C {noconn.sym} 120 -320 2 0 {name=l5}
diff --git a/xschem_library/logic/mux21.sym b/xschem_library/logic/mux21.sym
new file mode 100644
index 00000000..b25c4a89
--- /dev/null
+++ b/xschem_library/logic/mux21.sym
@@ -0,0 +1,49 @@
+v {xschem version=3.4.6RC file_version=1.2
+*
+* This file is part of XSCHEM,
+* a schematic capture and Spice/Vhdl/Verilog netlisting tool for circuit
+* simulation.
+* Copyright (C) 1998-2023 Stefan Frederik Schippers
+*
+* This program is free software; you can redistribute it and/or modify
+* it under the terms of the GNU General Public License as published by
+* the Free Software Foundation; either version 2 of the License, or
+* (at your option) any later version.
+*
+* This program is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+* GNU General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License
+* along with this program; if not, write to the Free Software
+* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+}
+G {}
+K {type=subcircuit
+vhdl_stop=true
+verilog_stop=true
+format="@name @pinlist @symname"
+template="name=x1 delay=\\"200 ps\\" del=200"
+generic_type="delay=time"}
+V {}
+S {}
+E {}
+L 4 -30 -30 30 -20 {}
+L 4 -30 30 30 20 {}
+L 4 -30 -30 -30 30 {}
+L 4 30 -20 30 20 {}
+L 4 -50 -20 -30 -20 {}
+L 4 30 0 50 0 {}
+L 4 -50 20 -30 20 {}
+L 4 0 25 0 50 {}
+B 5 -52.5 -22.5 -47.5 -17.5 {name=A dir=in}
+B 5 47.5 -2.5 52.5 2.5 {name=Z dir=out}
+B 5 -52.5 17.5 -47.5 22.5 {name=B dir=in}
+B 5 -2.5 47.5 2.5 52.5 {name=S dir=in}
+T {@symname} -62.5 -56 0 0 0.3 0.3 {}
+T {@name} 35 -42 0 0 0.2 0.2 {}
+T {A} -25 -24 0 0 0.2 0.2 {}
+T {Z} 25 -4 0 1 0.2 0.2 {}
+T {B} -25 16 0 0 0.2 0.2 {}
+T {S} -5 11 0 0 0.2 0.2 {}
diff --git a/xschem_library/logic/testbench.sch b/xschem_library/logic/testbench.sch
index f42c522d..9cd608a0 100644
--- a/xschem_library/logic/testbench.sch
+++ b/xschem_library/logic/testbench.sch
@@ -1,4 +1,4 @@
-v {xschem version=3.4.4 file_version=1.2
+v {xschem version=3.4.6RC file_version=1.2
 *
 * This file is part of XSCHEM,
 * a schematic capture and Spice/Vhdl/Verilog netlisting tool for circuit
@@ -102,32 +102,28 @@ V {integer n = 0;
 initial begin
   $dumpfile("dumpfile.vcd");
   $dumpvars(0, testbench);
-  A=0;
-  B=0;
+  RST=1;
+  A = 0;
+  B = 0;
   #1000;
-  A=1;
-  #1000;
-  B=1;
-  #1000;
-  A=0;
-  #1000;
-  B=0;
-  #1000;
-  B=1;
-  #1000;
-  B=0;
-  A=0;
-  #1000;
-  B=1;
-  #1000;
-  A=1;
-  #20000;
-  A=0;
+  RST=0;
+end
+
+
+
+always begin
+  #1013;
+  A = ~A;
+end
+
+always begin
+  #717;
+  B = ~B;
 end
 
 always begin
   if(n ==0 ) CK = 0;
-  if(n == 23) $finish;
+  if(n == 213) $finish;
   n = n + 1;
   #5000;
   CK = !CK;
@@ -185,6 +181,7 @@ end
 }
 S {}
 E {}
+T {Double edge triggered Flip FLop} 1090 -660 0 0 0.5 0.5 {}
 N 440 -350 470 -350 {lab=A}
 N 440 -310 470 -310 {lab=B}
 N 570 -330 600 -330 {lab=Y_NOR}
@@ -200,6 +197,18 @@ N 810 -360 840 -360 {lab=A}
 N 920 -360 950 -360 {lab=Y_BUF}
 N 780 -90 810 -90 {lab=B}
 N 890 -90 920 -90 {lab=BN}
+N 1300 -430 1310 -430 {lab=#net1}
+N 1300 -570 1310 -570 {lab=#net2}
+N 1350 -550 1380 -550 {lab=AL1}
+N 1350 -610 1350 -550 {lab=AL1}
+N 1300 -610 1350 -610 {lab=AL1}
+N 1350 -510 1380 -510 {lab=AL2}
+N 1350 -510 1350 -470 {lab=AL2}
+N 1300 -470 1350 -470 {lab=AL2}
+N 1080 -570 1170 -570 {lab=CK}
+N 1080 -610 1160 -610 {lab=A}
+N 1110 -470 1160 -470 {lab=A}
+N 1110 -610 1110 -470 {lab=A}
 C {title.sym} 160 -30 0 0 {name=l2}
 C {nr2.sym} 510 -330 0 0 {name=x1 }
 C {lab_pin.sym} 440 -350 2 1 {name=p20 lab=A}
@@ -281,3 +290,20 @@ C {adc_bridge.sym} 190 -260 0 0 {name=v6 delay=1}
 C {adc_bridge.sym} 190 -240 0 0 {name=v7 delay=1}
 C {adc_bridge.sym} 190 -220 0 0 {name=v8 delay=1}
 C {adc_bridge.sym} 190 -200 0 0 {name=v9 delay=1}
+C {mux21.sym} 1430 -530 0 0 {name=x10 del=200}
+C {lab_pin.sym} 1480 -530 0 1 {name=p57 lab=ZMUX}
+C {lab_pin.sym} 1430 -480 0 0 {name=p59 lab=CK}
+C {latch.sym} 1230 -590 0 0 {name=x11 del=200}
+C {latch.sym} 1230 -450 0 0 {name=x12 del=200}
+C {iv.sym} 1120 -430 0 0 {name=x13 del=1}
+C {lab_pin.sym} 1080 -570 0 0 {name=p60 lab=CK verilog_type=reg}
+C {lab_pin.sym} 1080 -430 0 0 {name=p61 lab=CK verilog_type=reg}
+C {lab_pin.sym} 220 -430 2 0 {name=p62 lab=RST verilog_type=reg}
+C {lab_pin.sym} 160 -430 2 1 {name=p63 lab=RST_A verilog_type=reg}
+C {adc_bridge.sym} 190 -430 0 0 {name=v10 delay=1
+lab=RST_A}
+C {lab_pin.sym} 1080 -610 0 0 {name=p64 lab=A}
+C {lab_pin.sym} 1230 -540 2 1 {name=p56 lab=RST verilog_type=reg}
+C {lab_pin.sym} 1230 -400 2 1 {name=p58 lab=RST verilog_type=reg}
+C {lab_pin.sym} 1350 -610 0 1 {name=p65 lab=AL1}
+C {lab_pin.sym} 1350 -470 0 1 {name=p66 lab=AL2}