diff --git a/src/kyupy/circuit.py b/src/kyupy/circuit.py
index 76d4738..65ebfbb 100644
--- a/src/kyupy/circuit.py
+++ b/src/kyupy/circuit.py
@@ -13,6 +13,8 @@ Circuit graphs also define an ordering of inputs, outputs and other nodes to eas
 from collections import deque, defaultdict
 import re
 
+import numpy as np
+
 
 class GrowingList(list):
     def __setitem__(self, index, value):
@@ -359,7 +361,7 @@ class Circuit:
         of the input and output ports must match the pins of the replaced node.
         """
         ios = set(impl.io_nodes)
-        impl_in_lines = [n.outs[0] for n in impl.io_nodes if len(n.ins) == 0]
+        impl_in_nodes = [n for n in impl.io_nodes if len(n.ins) == 0]
         impl_out_lines = [n.ins[0] for n in impl.io_nodes if len(n.ins) > 0]
         designated_cell = None
         if len(impl_out_lines) > 0:
@@ -367,9 +369,9 @@ class Circuit:
             while n.kind == '__fork__' and n not in ios:
                 n = n.ins[0].driver
             designated_cell = n
-        node_in_lines = list(node.ins) + [None] * (len(impl_in_lines)-len(node.ins))
+        node_in_lines = list(node.ins) + [None] * (len(impl_in_nodes)-len(node.ins))
         node_out_lines = list(node.outs) + [None] * (len(impl_out_lines)-len(node.outs))
-        assert len(node_in_lines) == len(impl_in_lines)
+        assert len(node_in_lines) == len(impl_in_nodes)
         assert len(node_out_lines) == len(impl_out_lines)
         node_map = dict()
         if designated_cell is not None:
@@ -386,13 +388,20 @@ class Circuit:
                     node_map[n] = Node(self, f'{node.name}~{n.name}', n.kind)
             elif len(n.outs) > 0 and len(n.ins) > 0:  # output is also read by impl. circuit, need to add a fork.
                 node_map[n] = Node(self, f'{node.name}~{n.name}')
+            elif len(n.ins) == 0 and len(n.outs) > 1:  # input is read by multiple nodes, need to add fork.
+                node_map[n] = Node(self, f'{node.name}~{n.name}')
         for l in impl.lines:  # add all internal lines to main circuit
             if l.reader in node_map and l.driver in node_map:
                 Line(self, (node_map[l.driver], l.driver_pin), (node_map[l.reader], l.reader_pin))
-        for l, ll in zip(impl_in_lines, node_in_lines):  # connect inputs
+        for inn, ll in zip(impl_in_nodes, node_in_lines):  # connect inputs
             if ll is None: continue
-            ll.reader = node_map[l.reader]
-            ll.reader_pin = l.reader_pin
+            if len(inn.outs) == 1:
+                l = inn.outs[0]
+                ll.reader = node_map[l.reader]
+                ll.reader_pin = l.reader_pin
+            else:
+                ll.reader = node_map[inn]  # connect to existing fork
+                ll.reader_pin = 0
             ll.reader.ins[ll.reader_pin] = ll
         for l, ll in zip(impl_out_lines, node_out_lines):  # connect outputs
             if ll is None:
@@ -467,7 +476,7 @@ class Circuit:
         Nodes without input lines and nodes whose :py:attr:`Node.kind` contains the
         substrings 'dff' or 'latch' are yielded first.
         """
-        visit_count = [0] * len(self.nodes)
+        visit_count = np.zeros(len(self.nodes), dtype=np.uint32)
         queue = deque(n for n in self.nodes if len(n.ins) == 0 or 'dff' in n.kind.lower() or 'latch' in n.kind.lower())
         while len(queue) > 0:
             n = queue.popleft()
@@ -479,6 +488,16 @@ class Circuit:
                     queue.append(succ)
             yield n
 
+    def topological_order_with_level(self):
+        level = np.zeros(len(self.nodes), dtype=np.int32) - 1
+        for n in self.topological_order():
+            if len(n.ins) == 0 or 'dff' in n.kind.lower() or 'latch' in n.kind.lower():
+                l = 0
+            else:
+                l = level[[l.driver.index for l in n.ins if l is not None]].max() + 1
+            level[n] = l
+            yield n, l
+
     def topological_line_order(self):
         """Generator function to iterate over all lines in topological order.
         """
@@ -540,3 +559,31 @@ class Circuit:
                 queue.extend(preds)
                 region.append(n)
             yield stem, region
+
+    def dot(self, format='svg'):
+        from graphviz import Digraph
+        dot = Digraph(format=format, graph_attr={'rankdir': 'LR', 'splines': 'true'})
+
+        node_level = np.zeros(len(self.nodes), dtype=np.uint32)
+        level_nodes = defaultdict(list)
+        for n, lv in self.topological_order_with_level():
+            level_nodes[lv].append(n)
+            node_level[n] = lv
+
+        for lv in level_nodes:
+            with dot.subgraph() as s:
+                s.attr(rank='same')
+                for n in level_nodes[lv]:
+                    ins = '|'.join([f'<i{i}>{i}' for i in range(len(n.ins))])
+                    outs = '|'.join([f'<o{i}>{i}' for i in range(len(n.outs))])
+                    s.node(name=str(n.index), label = f'{{{{{ins}}}|{n.index}\n{n.kind}\n{n.name}|{{{outs}}}}}', shape='record')
+
+        for l in self.lines:
+            driver, reader = f'{l.driver.index}:o{l.driver_pin}', f'{l.reader.index}:i{l.reader_pin}'
+            if node_level[l.driver] >= node_level[l.reader]:
+                dot.edge(driver, reader, style='dotted', label=str(l.index))
+                pass
+            else:
+                dot.edge(driver, reader, label=str(l.index))
+
+        return dot