diff --git a/src/dsp/mod.rs b/src/dsp/mod.rs
index 0e0cc72..24f3258 100644
--- a/src/dsp/mod.rs
+++ b/src/dsp/mod.rs
@@ -81,6 +81,9 @@ pub const MAX_BLOCK_SIZE : usize = 128;
 /// currently executed node.
 /// This structure is created by the [crate::nodes::NodeExecutor] on the fly.
 pub struct NodeContext<'a> {
+    /// The bitmask that indicates which input ports are used/connected
+    /// to some output.
+    pub in_connected:  u64,
     /// The bitmask that indicates which output ports are used/connected
     /// to some input.
     pub out_connected:  u64,
@@ -1161,6 +1164,15 @@ macro_rules! make_node_info_enum {
             })+
         }
 
+        #[allow(non_snake_case)]
+        pub mod is_in_con {
+            $(pub mod $variant {
+                $(#[inline] pub fn $para(nctx: &crate::dsp::NodeContext) -> bool {
+                    nctx.in_connected & (1 << $in_idx) != 0x0
+                })*
+            })+
+        }
+
         mod ni {
             $(
                 #[derive(Debug, Clone)]
diff --git a/src/dsp/node_test.rs b/src/dsp/node_test.rs
index 3a5f58c..5c6a057 100644
--- a/src/dsp/node_test.rs
+++ b/src/dsp/node_test.rs
@@ -50,7 +50,7 @@ impl Test {
     pub const sig : &'static str = "Test sig\nThe output of p as signal";
     pub const tsig : &'static str = "Test tsig\nA short trigger pulse will be generated when the 'trig' input is triggered.";
     pub const out2 : &'static str = "Test out2\nA test output that will emit 1.0 if output 'sig' is connected.";
-    pub const out3 : &'static str = "Test out3\n";
+    pub const out3 : &'static str = "Test out3\nA test output that will emit 1.0 if input 'f' is connected.";
     pub const out4 : &'static str = "Test out4\n";
     pub const outc : &'static str = "Test outc\nEmits a number that defines the out_connected bitmask. Used only for testing!";
 
@@ -77,13 +77,14 @@ impl DspNode for Test {
         atoms: &[SAtom], _inputs: &[ProcBuf],
         outputs: &mut [ProcBuf], _led: LedPhaseVals)
     {
-        use crate::dsp::{out_idx, at, is_out_con, out_buf};
+        use crate::dsp::{out_idx, at, is_out_con, out_buf, is_in_con};
 
         let p     = at::Test::p(atoms);
         let trig  = at::Test::trig(atoms);
         let tsig  = out_idx::Test::tsig();
 
         let mut out2  = out_buf::Test::out2(outputs);
+        let mut out3  = out_buf::Test::out3(outputs);
         let mut outc  = out_buf::Test::outc(outputs);
 
         let (out, tsig) = outputs.split_at_mut(tsig);
@@ -113,6 +114,8 @@ impl DspNode for Test {
 
             out2.write(frame,
                 if is_out_con::Test::sig(nctx) { 1.0 } else { 0.0 });
+            out3.write(frame,
+                if is_in_con::Test::f(nctx) { 1.0 } else { 0.0 });
             outc.write(frame, nctx.out_connected as f32);
         }
     }
diff --git a/src/matrix.rs b/src/matrix.rs
index 2d84c7b..d038084 100644
--- a/src/matrix.rs
+++ b/src/matrix.rs
@@ -1054,9 +1054,9 @@ mod tests {
         assert!(nodes[2].to_id(2) == NodeId::Sin(2));
 
         let prog = node_exec.get_prog();
-        assert_eq!(prog.prog[0].to_string(), "Op(i=0 out=(0-1|1) in=(0-2) at=(0-0) mod=(0-0))");
-        assert_eq!(prog.prog[1].to_string(), "Op(i=1 out=(1-2|1) in=(2-4) at=(0-0) mod=(0-0) cpy=(o0 => i2))");
-        assert_eq!(prog.prog[2].to_string(), "Op(i=2 out=(2-3|0) in=(4-6) at=(0-0) mod=(0-0) cpy=(o1 => i4))");
+        assert_eq!(prog.prog[0].to_string(), "Op(i=0 out=(0-1|1) in=(0-2|0) at=(0-0) mod=(0-0))");
+        assert_eq!(prog.prog[1].to_string(), "Op(i=1 out=(1-2|1) in=(2-4|1) at=(0-0) mod=(0-0) cpy=(o0 => i2))");
+        assert_eq!(prog.prog[2].to_string(), "Op(i=2 out=(2-3|0) in=(4-6|1) at=(0-0) mod=(0-0) cpy=(o1 => i4))");
     }
 
     #[test]
@@ -1146,8 +1146,8 @@ mod tests {
 
         let prog = node_exec.get_prog();
         assert_eq!(prog.prog.len(), 2);
-        assert_eq!(prog.prog[0].to_string(), "Op(i=0 out=(0-1|1) in=(0-2) at=(0-0) mod=(0-0))");
-        assert_eq!(prog.prog[1].to_string(), "Op(i=1 out=(1-1|0) in=(2-5) at=(0-1) mod=(0-0) cpy=(o0 => i2))");
+        assert_eq!(prog.prog[0].to_string(), "Op(i=0 out=(0-1|1) in=(0-2|0) at=(0-0) mod=(0-0))");
+        assert_eq!(prog.prog[1].to_string(), "Op(i=1 out=(1-1|0) in=(2-5|1) at=(0-1) mod=(0-0) cpy=(o0 => i2))");
     }
 
     #[test]
@@ -1177,8 +1177,8 @@ mod tests {
 
         let prog = node_exec.get_prog();
         assert_eq!(prog.prog.len(), 2);
-        assert_eq!(prog.prog[0].to_string(), "Op(i=2 out=(2-3|1) in=(4-6) at=(0-0) mod=(0-0))");
-        assert_eq!(prog.prog[1].to_string(), "Op(i=3 out=(3-3|0) in=(6-9) at=(0-1) mod=(0-0) cpy=(o2 => i6))");
+        assert_eq!(prog.prog[0].to_string(), "Op(i=2 out=(2-3|1) in=(4-6|0) at=(0-0) mod=(0-0))");
+        assert_eq!(prog.prog[1].to_string(), "Op(i=3 out=(3-3|0) in=(6-9|1) at=(0-1) mod=(0-0) cpy=(o2 => i6))");
     }
 
     #[test]
@@ -1278,10 +1278,10 @@ mod tests {
         node_exec.process_graph_updates();
 
         let prog = node_exec.get_prog();
-        assert_eq!(prog.prog[0].to_string(), "Op(i=0 out=(0-1|1) in=(0-2) at=(0-0) mod=(0-1))");
-        assert_eq!(prog.prog[1].to_string(), "Op(i=3 out=(3-4|1) in=(6-8) at=(0-0) mod=(5-5))");
-        assert_eq!(prog.prog[2].to_string(), "Op(i=1 out=(1-2|1) in=(2-4) at=(0-0) mod=(1-3) cpy=(o0 => i2) mod=1)");
-        assert_eq!(prog.prog[3].to_string(), "Op(i=2 out=(2-3|0) in=(4-6) at=(0-0) mod=(3-5) cpy=(o1 => i4) cpy=(o3 => i5) mod=3 mod=4)");
+        assert_eq!(prog.prog[0].to_string(), "Op(i=0 out=(0-1|1) in=(0-2|0) at=(0-0) mod=(0-1))");
+        assert_eq!(prog.prog[1].to_string(), "Op(i=3 out=(3-4|1) in=(6-8|0) at=(0-0) mod=(5-5))");
+        assert_eq!(prog.prog[2].to_string(), "Op(i=1 out=(1-2|1) in=(2-4|1) at=(0-0) mod=(1-3) cpy=(o0 => i2) mod=1)");
+        assert_eq!(prog.prog[3].to_string(), "Op(i=2 out=(2-3|0) in=(4-6|3) at=(0-0) mod=(3-5) cpy=(o1 => i4) cpy=(o3 => i5) mod=3 mod=4)");
     }
 
     #[test]
@@ -1315,8 +1315,8 @@ mod tests {
         node_exec.process_graph_updates();
 
         let prog = node_exec.get_prog();
-        assert_eq!(prog.prog[0].to_string(), "Op(i=0 out=(0-1|1) in=(0-2) at=(0-0) mod=(0-1))");
-        assert_eq!(prog.prog[1].to_string(), "Op(i=1 out=(1-2|1) in=(2-4) at=(0-0) mod=(1-3) cpy=(o0 => i2) mod=1)");
-        assert_eq!(prog.prog[2].to_string(), "Op(i=2 out=(2-3|0) in=(4-6) at=(0-0) mod=(3-3) cpy=(o1 => i4))");
+        assert_eq!(prog.prog[0].to_string(), "Op(i=0 out=(0-1|1) in=(0-2|0) at=(0-0) mod=(0-1))");
+        assert_eq!(prog.prog[1].to_string(), "Op(i=1 out=(1-2|1) in=(2-4|1) at=(0-0) mod=(1-3) cpy=(o0 => i2) mod=1)");
+        assert_eq!(prog.prog[2].to_string(), "Op(i=2 out=(2-3|0) in=(4-6|1) at=(0-0) mod=(3-3) cpy=(o1 => i4))");
     }
 }
diff --git a/src/nodes/node_conf.rs b/src/nodes/node_conf.rs
index fc0f52c..47a0db8 100644
--- a/src/nodes/node_conf.rs
+++ b/src/nodes/node_conf.rs
@@ -81,6 +81,7 @@ impl NodeInstance {
             at_idxlen:      (self.at_start, self.at_end),
             mod_idxlen:     (self.mod_start, self.mod_end),
             out_connected:  0x0,
+            in_connected:   0x0,
             inputs:         vec![],
         }
     }
diff --git a/src/nodes/node_exec.rs b/src/nodes/node_exec.rs
index 91b11bc..46978b1 100644
--- a/src/nodes/node_exec.rs
+++ b/src/nodes/node_exec.rs
@@ -449,6 +449,7 @@ impl NodeExecutor {
                     exec_ctx,
                     &NodeContext {
                         out_connected: op.out_connected,
+                        in_connected:  op.in_connected,
                         params:        &prog.inp[inp.0..inp.1],
                     },
                     &prog.atoms[at.0..at.1],
diff --git a/src/nodes/node_prog.rs b/src/nodes/node_prog.rs
index 4f5b119..01859f0 100644
--- a/src/nodes/node_prog.rs
+++ b/src/nodes/node_prog.rs
@@ -81,12 +81,29 @@ pub struct NodeOp {
     /// (<out vec index>, <own node input index>,
     ///  (<mod index into NodeProg::modops>, <mod amt>))
     pub inputs: Vec<(usize, usize, Option<usize>)>,
+    /// A bit mask which indicates which of the input ports are actually
+    /// used/connected to some output.
+    pub in_connected: u64,
     /// A bit mask which indicates which of the output ports are actually
     /// used/connected to some input.
     pub out_connected: u64,
 }
 
 impl NodeOp {
+    pub fn in_idx_belongs_to_nodeop(&self, idx: usize) -> bool {
+           idx >= self.in_idxlen.0
+        && idx <  self.in_idxlen.1
+    }
+
+    pub fn set_in_idx_connected_flag(&mut self, global_idx: usize) {
+        if !self.in_idx_belongs_to_nodeop(global_idx) {
+            return;
+        }
+
+        let local_idx = global_idx - self.in_idxlen.0;
+        self.in_connected |= 0x1 << local_idx;
+    }
+
     pub fn out_idx_belongs_to_nodeop(&self, idx: usize) -> bool {
            idx >= self.out_idxlen.0
         && idx <  self.out_idxlen.1
@@ -104,13 +121,14 @@ impl NodeOp {
 
 impl std::fmt::Display for NodeOp {
     fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "Op(i={} out=({}-{}|{:x}) in=({}-{}) at=({}-{}) mod=({}-{})",
+        write!(f, "Op(i={} out=({}-{}|{:x}) in=({}-{}|{:x}) at=({}-{}) mod=({}-{})",
                self.idx,
                self.out_idxlen.0,
                self.out_idxlen.1,
                self.out_connected,
                self.in_idxlen.0,
                self.in_idxlen.1,
+               self.in_connected,
                self.at_idxlen.0,
                self.at_idxlen.1,
                self.mod_idxlen.0,
@@ -264,6 +282,7 @@ impl NodeProg {
         }
 
         node_op.out_connected = 0x0;
+        node_op.in_connected  = 0x0;
         self.prog.push(node_op);
     }
 
@@ -282,6 +301,7 @@ impl NodeProg {
 
         for n_op in self.prog.iter_mut() {
             if n_op.idx == node_op.idx {
+                n_op.set_in_idx_connected_flag(inp_index);
                 n_op.inputs.push((out_index, inp_index, mod_index));
                 return;
             }
diff --git a/tests/node_test.rs b/tests/node_test.rs
index 42ff0a3..80cbcff 100644
--- a/tests/node_test.rs
+++ b/tests/node_test.rs
@@ -79,3 +79,30 @@ fn check_node_test_out_connected() {
     assert_decimated_feq!(res.0, 1, vec![ mask as f32; 10 ]);
     assert_decimated_feq!(res.1, 1, vec![ 0.0; 10 ]);
 }
+
+#[test]
+fn check_node_test_in_connected() {
+    let (node_conf, mut node_exec) = new_node_engine();
+    let mut matrix = Matrix::new(node_conf, 6, 3);
+
+    let test = NodeId::Test(0);
+    let tst2 = NodeId::Test(1);
+    let out  = NodeId::Out(0);
+    matrix.place(0, 0, Cell::empty(test)
+                       .out(None, None, test.out("sig")));
+    matrix.place(0, 1, Cell::empty(tst2)
+                       .input(tst2.inp("f"), None, None)
+                       .out(None, None, test.out("out3")));
+    matrix.place(0, 2, Cell::empty(out)
+                       .input(out.inp("ch1"), None, None));
+    matrix.sync().unwrap();
+
+    let res = run_for_ms(&mut node_exec, 2.0);
+    assert_decimated_feq!(res.0, 1, vec![ 1.0; 10 ]);
+
+    matrix.place(0, 0, Cell::empty(NodeId::Nop));
+    matrix.sync().unwrap();
+
+    let res = run_for_ms(&mut node_exec, 2.0);
+    assert_decimated_feq!(res.0, 1, vec![ 0.0; 10 ]);
+}