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diff --git a/src/pathsim_chem/tritium/bubbler.py b/src/pathsim_chem/tritium/bubbler.py
index fc39a53..955b633 100644
--- a/src/pathsim_chem/tritium/bubbler.py
+++ b/src/pathsim_chem/tritium/bubbler.py
@@ -10,6 +10,7 @@
 
 from pathsim.blocks.dynsys import DynamicalSystem
 from pathsim.events.schedule import ScheduleList
+from pathsim.utils.register import Register
 
 
 # BLOCK DEFIINITIONS ====================================================================
@@ -92,18 +93,6 @@ class Bubbler4(DynamicalSystem):
     of a full vial with an empty one.
     """
 
-    _port_map_out = {
-        "vial1": 0,
-        "vial2": 1,
-        "vial3": 2,
-        "vial4": 3,
-        "sample_out": 4,
-    }
-    _port_map_in = {
-        "sample_in_soluble": 0,
-        "sample_in_insoluble": 1,
-    }
-
     def __init__(
         self,
         conversion_efficiency=0.9,
@@ -149,7 +138,30 @@ def _fn_a(x, u, t):
             return np.hstack([x, sample_out])
 
         #initialization just like `DynamicalSystem` block
-        super().__init__(func_dyn=_fn_d, func_alg=_fn_a, initial_value=np.zeros(4))
+        super().__init__(
+            func_dyn=_fn_d, 
+            func_alg=_fn_a, 
+            initial_value=np.zeros(4),
+            )
+
+        # define port maps 
+        self.inputs = Register(
+            size=2, 
+            mapping={
+                "sample_in_soluble": 0,
+                "sample_in_insoluble": 1,
+                },
+            )
+        self.outputs = Register(
+            size=5, 
+            mapping={
+                "vial1": 0,
+                "vial2": 1,
+                "vial3": 2,
+                "vial4": 3,
+                "sample_out": 4,
+                },
+            )
 
         #create internal vial reset events
         self._create_reset_events()
diff --git a/src/pathsim_chem/tritium/residencetime.py b/src/pathsim_chem/tritium/residencetime.py
index 10707fc..c06e797 100644
--- a/src/pathsim_chem/tritium/residencetime.py
+++ b/src/pathsim_chem/tritium/residencetime.py
@@ -9,7 +9,7 @@
 import numpy as np
 
 from pathsim.blocks.dynsys import DynamicalSystem
-
+from pathsim.utils.register import Register
 
 # BLOCKS ================================================================================
 
@@ -50,30 +50,35 @@ class ResidenceTime(DynamicalSystem):
 
     def __init__(self, tau=1, betas=None, gammas=None, initial_value=0, source_term=0):
 
-        #input validation
+        # input validation
         if np.isclose(tau, 0):
             raise ValueError(f"'tau' must be nonzero but is {tau}")
     
-        #time constant and input/output weights
+        # time constant and input/output weights
         self.tau = tau
         self.betas = 1 if betas is None else np.array(betas)
         self.gammas = 1 if gammas is None else np.array(gammas)
         self.source_term = source_term
 
-        #rhs of residence time ode
+        # rhs of residence time ode
         def _fn_d(x, u, t):
             return -x/self.tau + self.source_term + sum(self.betas*u)
 
-        #jacobian of rhs wrt x
+        # jacobian of rhs wrt x
         def _jc_d(x, u, t):
             return -1/self.tau
 
-        #output function of residence time ode
+        # output function of residence time ode
         def _fn_a(x, u, t):
             return self.gammas * x
 
-        #initialization just like `DynamicalSystem` block
-        super().__init__(func_dyn=_fn_d, jac_dyn=_jc_d, func_alg=_fn_a, initial_value=initial_value)
+        # initialization just like `DynamicalSystem` block
+        super().__init__(
+            func_dyn=_fn_d, 
+            jac_dyn=_jc_d, 
+            func_alg=_fn_a, 
+            initial_value=initial_value,
+            )
 
 
 class Process(ResidenceTime):
@@ -112,11 +117,11 @@ class Process(ResidenceTime):
         constant source term / generation term of the process
     """
 
-    #max number of ports
-    _n_out_max = 2
-
-    #maps for input and output port labels
-    _port_map_out = {"x": 0, "x/tau": 1}
-
     def __init__(self, tau=1, initial_value=0, source_term=0):
         super().__init__(tau, 1, [1, 1/tau], initial_value, source_term)
+
+        # define output port maps based on fractions
+        self.outputs = Register(
+            size=2, 
+            mapping={"x": 0, "x/tau": 1}
+            )
\ No newline at end of file
diff --git a/src/pathsim_chem/tritium/splitter.py b/src/pathsim_chem/tritium/splitter.py
index fa55cb0..ee4ebbd 100644
--- a/src/pathsim_chem/tritium/splitter.py
+++ b/src/pathsim_chem/tritium/splitter.py
@@ -9,6 +9,7 @@
 import numpy as np
 
 from pathsim.blocks.function import Function
+from pathsim.utils.register import Register
 
 
 # BLOCKS ================================================================================
@@ -28,22 +29,23 @@ class Splitter(Function):
         must sum up to one
     """
 
-    #max number of ports
-    _n_in_max = 1
-
-    #maps for input and output port labels
-    _port_map_in = {"in": 0}
-    
     def __init__(self, fractions=None):
 
         self.fractions = np.ones(1) if fractions is None else np.array(fractions)
 
-        #input validation
+        # input validation
         if not np.isclose(sum(self.fractions), 1):
             raise ValueError(f"'fractions' must sum to one and not {sum(self.fractions)}")
 
-        #initialize like `Function` block
+        # initialize like `Function` block
         super().__init__(func=lambda u: self.fractions*u)
 
-        #dynamically define output port map based on fractions
-        self._port_map_out = {f"out {fr}": i for i, fr in enumerate(self.fractions)}
+        # define port maps based on fractions
+        self.inputs = Register(
+            size=1, 
+            mapping={"in": 0}
+            )
+        self.outputs = Register(
+            size=len(self.fractions), 
+            mapping={f"out {fr}": i for i, fr in enumerate(self.fractions)}
+            )
\ No newline at end of file
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