diff --git a/myhdl/_ShadowSignal.py b/myhdl/_ShadowSignal.py
index 299e36f2..099f68c9 100644
--- a/myhdl/_ShadowSignal.py
+++ b/myhdl/_ShadowSignal.py
@@ -23,13 +23,19 @@
 """
 
 from myhdl._Signal import _Signal
+from myhdl._Waiter import _SignalWaiter, _SignalTupleWaiter
+from myhdl._intbv import intbv
 
 # shadow signals
         
         
 class _ShadowSignal(_Signal):
 
-    __slots__ = ('gen', )
+    __slots__ = ('gen', 'waiter')
+
+    def __init__(self, val):
+        _Signal.__init__(self, val)
+        self.driven = True
 
 
         
@@ -40,9 +46,9 @@ class _SliceSignal(_ShadowSignal):
     def __init__(self, sig, left, right=None):
         ### XXX error checks
         if right is None:
-            _Signal.__init__(self, sig[left])
+            _ShadowSignal.__init__(self, sig[left])
         else:
-            _Signal.__init__(self, sig[left:right])
+            _ShadowSignal.__init__(self, sig[left:right])
         self.sig = sig
         self.left = left
         self.right = right
@@ -50,7 +56,7 @@ class _SliceSignal(_ShadowSignal):
             self.gen = self.genfuncIndex()
         else:
             self.gen = self.genfuncSlice()
-        self._driven = True
+        self.waiter = _SignalWaiter(self.gen)
 
     def genfuncIndex(self):
         sig, index = self.sig, self.left
@@ -77,3 +83,42 @@ class _SliceSignal(_ShadowSignal):
             return "%s <= %s(%s);" % (self._name, self.sig._name, self.left)
         else:
             return "%s <= %s(%s-1 downto %s);" % (self._name, self.sig._name, self.left, self.right)
+
+
+
+class ConcatSignal(_ShadowSignal):
+
+    __slots__ = ('_args',)
+
+    def __init__(self, *args):
+        assert len(args) >= 2
+        self._args = args
+        ### XXX error checks
+        nrbits = 0
+        for a in args:
+            nrbits += len(a)
+        ini = intbv(0)[nrbits:]
+        hi = nrbits
+        for a in args:
+            lo = hi - len(a)
+            ini[hi:lo] = a
+            hi = lo
+        _ShadowSignal.__init__(self, ini)
+        self.gen = self.genfunc()
+        self.waiter = _SignalTupleWaiter(self.gen)
+
+    def genfunc(self):
+        set_next = _Signal._set_next
+        args = self._args
+        nrbits = self._nrbits
+        newval = intbv(0)[nrbits:]
+        while 1:
+            hi = nrbits
+            for a in args:
+                lo = hi - len(a)
+                newval[hi:lo] = a
+                hi = lo
+            set_next(self, newval)
+            yield args
+                
+
diff --git a/myhdl/_Simulation.py b/myhdl/_Simulation.py
index 6046798d..34b39fd4 100644
--- a/myhdl/_Simulation.py
+++ b/myhdl/_Simulation.py
@@ -224,10 +224,9 @@ def _makeWaiters(arglist):
             raise SimulationError(_error.DuplicatedArg)
         ids.add(id(arg))
     # add waiters for shadow signals
-    # waiter wrapping done here to avoid circular imports
     for sig in _signals:
         if not isinstance(sig, _ShadowSignal):
             continue
-        waiters.append(_SignalWaiter(sig.gen))
+        waiters.append(sig.waiter)
     return waiters, cosim
         
diff --git a/myhdl/__init__.py b/myhdl/__init__.py
index d26e661a..39dfa355 100644
--- a/myhdl/__init__.py
+++ b/myhdl/__init__.py
@@ -24,6 +24,7 @@ Simulation -- simulation class
 StopStimulation -- exception that stops a simulation
 now -- function that returns the current time
 Signal -- class to model hardware signals
+ConcatSignal -- class that models a concatenation shadow signal
 delay -- callable to model delay in a yield statement
 posedge -- callable to model a rising edge on a signal in a yield statement
 negedge -- callable to model a falling edge on a signal in a yield statement
@@ -36,7 +37,6 @@ bin -- returns a binary string representation.
 concat -- function to concat ints, bitstrings, bools, intbvs, Signals
        -- returns an intbv
 instances -- function that returns all instances defined in a function
-processes -- function that returns all processes defined in a function
 always_comb -- function that returns an input-sensitive generator
 enum -- function that returns an enumeration type
 traceSignals -- function that enables signal tracing in a VCD file
@@ -110,6 +110,7 @@ from _concat import concat
 from _intbv import intbv
 from _join import join
 from _Signal import posedge, negedge, Signal
+from _ShadowSignal import ConcatSignal
 from _simulator import now
 from _delay import delay
 from _Cosimulation import Cosimulation
@@ -135,6 +136,7 @@ __all__ = ["bin",
            "posedge",
            "negedge",
            "Signal",
+           "ConcatSignal",
            "now",
            "delay",
            "downrange",
diff --git a/myhdl/test/core2/test_ShadowSignal.py b/myhdl/test/core2/test_ShadowSignal.py
index cdfd3964..9c09adc1 100644
--- a/myhdl/test/core2/test_ShadowSignal.py
+++ b/myhdl/test/core2/test_ShadowSignal.py
@@ -1,6 +1,6 @@
 from myhdl import *
 
-def bench_ShadowSignal():
+def bench_SliceSignal():
     
     s = Signal(intbv(0)[8:])
     a, b, c = s(7), s(5), s(0)
@@ -22,6 +22,41 @@ def bench_ShadowSignal():
     return check
 
 
-def test_ShadowSignal():
-    Simulation(bench_ShadowSignal()).run()
+def test_SliceSignal():
+    Simulation(bench_SliceSignal()).run()
+
+
+def bench_ConcatSignal():
+    
+    a = Signal(intbv(0)[8:])
+    b = Signal(bool(0))
+    c = Signal(intbv(0)[3:])
+    d = Signal(intbv(0)[4:])
+    
+    s = ConcatSignal(a, b, c, d)
+
+    @instance
+    def check():
+        for i in range(2**len(a)):
+            for j in (0, 1):
+                for k in range(len(c)):
+                    for m in range(len(d)):
+                        a.next = i
+                        b.next = j
+                        c.next = k
+                        d.next = m
+                        yield delay(10)
+                        assert s[16:8] == a
+                        assert s[7] == b
+                        assert s[7:4] == c
+                        assert s[4:] == d
+
+    return check
+
+
+def test_ConcatSignal():
+    Simulation(bench_ConcatSignal()).run()
+
+
+