diff --git a/libopenfpga/libarchopenfpga/src/pb_type_annotation.cpp b/libopenfpga/libarchopenfpga/src/pb_type_annotation.cpp
index da494f77f..d04e39b72 100644
--- a/libopenfpga/libarchopenfpga/src/pb_type_annotation.cpp
+++ b/libopenfpga/libarchopenfpga/src/pb_type_annotation.cpp
@@ -61,7 +61,7 @@ std::string PbTypeAnnotation::idle_mode_name() const {
   return idle_mode_name_;
 }
 
-std::string PbTypeAnnotation::mode_bits() const {
+std::vector<size_t> PbTypeAnnotation::mode_bits() const {
   return mode_bits_;
 }
 
@@ -155,7 +155,7 @@ void PbTypeAnnotation::set_idle_mode_name(const std::string& name) {
   idle_mode_name_ = name;
 }
 
-void PbTypeAnnotation::set_mode_bits(const std::string& mode_bits) {
+void PbTypeAnnotation::set_mode_bits(const std::vector<size_t>& mode_bits) {
   mode_bits_ = mode_bits;
 }
 
diff --git a/libopenfpga/libarchopenfpga/src/pb_type_annotation.h b/libopenfpga/libarchopenfpga/src/pb_type_annotation.h
index e03201cde..a969ee93d 100644
--- a/libopenfpga/libarchopenfpga/src/pb_type_annotation.h
+++ b/libopenfpga/libarchopenfpga/src/pb_type_annotation.h
@@ -43,7 +43,7 @@ class PbTypeAnnotation {
     bool is_physical_pb_type() const;
     std::string physical_mode_name() const;
     std::string idle_mode_name() const;
-    std::string mode_bits() const;
+    std::vector<size_t> mode_bits() const;
     std::string circuit_model_name() const;
     int physical_pb_type_index_factor() const;
     int physical_pb_type_index_offset() const;
@@ -61,7 +61,7 @@ class PbTypeAnnotation {
     void set_physical_parent_mode_names(const std::vector<std::string>& names);
     void set_physical_mode_name(const std::string& name);
     void set_idle_mode_name(const std::string& name);
-    void set_mode_bits(const std::string& mode_bits);
+    void set_mode_bits(const std::vector<size_t>& mode_bits);
     void set_circuit_model_name(const std::string& name);
     void set_physical_pb_type_index_factor(const int& value);
     void set_physical_pb_type_index_offset(const int& value);
@@ -102,7 +102,7 @@ class PbTypeAnnotation {
     std::string idle_mode_name_;
 
     /* Configuration bits to select an operting mode for the circuit mode name */
-    std::string mode_bits_;
+    std::vector<size_t> mode_bits_;
 
     /* Circuit mode name linked to a physical pb_type.
      * This is only applicable to the physical pb_type
diff --git a/libopenfpga/libarchopenfpga/src/read_xml_pb_type_annotation.cpp b/libopenfpga/libarchopenfpga/src/read_xml_pb_type_annotation.cpp
index 253053bf5..a17e970b7 100644
--- a/libopenfpga/libarchopenfpga/src/read_xml_pb_type_annotation.cpp
+++ b/libopenfpga/libarchopenfpga/src/read_xml_pb_type_annotation.cpp
@@ -63,6 +63,31 @@ void read_xml_pb_port_annotation(pugi::xml_node& xml_port,
   pb_type_annotation.set_physical_pin_rotate_offset(name_attr, get_attribute(xml_port, "physical_mode_pin_rotate_offset", loc_data, pugiutil::ReqOpt::OPTIONAL).as_int(0));
 }
 
+/********************************************************************
+ * Parse mode_bits: convert from string to array of digits
+ * We only allow the bit to either '0' or '1'
+ *******************************************************************/
+static 
+std::vector<size_t> parse_mode_bits(pugi::xml_node& xml_mode_bits,
+                                    const pugiutil::loc_data& loc_data,
+                                    const std::string& mode_bit_str) {
+  std::vector<size_t> mode_bits;
+
+  for (const char& bit_char : mode_bit_str) {
+    if ('0' == bit_char) {
+      mode_bits.push_back(0);
+    } else if ('1' == bit_char) {
+      mode_bits.push_back(1);
+    } else {
+      archfpga_throw(loc_data.filename_c_str(), loc_data.line(xml_mode_bits),
+                     "Unexpected '%c' character found in the mode bit '%s'! Only allow either '0' or '1'\n",
+                     bit_char, mode_bit_str.c_str());
+    }
+  } 
+
+  return mode_bits;
+}
+
 /********************************************************************
  * Parse XML description for a pb_type annotation under a <pb_type> XML node
  *******************************************************************/
@@ -119,7 +144,8 @@ void read_xml_pb_type_annotation(pugi::xml_node& xml_pb_type,
   pb_type_annotation.set_idle_mode_name(get_attribute(xml_pb_type, "idle_mode_name", loc_data, pugiutil::ReqOpt::OPTIONAL).as_string());
 
   /* Parse mode bits which are applied to both pb_types */
-  pb_type_annotation.set_mode_bits(get_attribute(xml_pb_type, "mode_bits", loc_data, pugiutil::ReqOpt::OPTIONAL).as_string());
+  std::vector<size_t> mode_bit_data = parse_mode_bits(xml_pb_type, loc_data, get_attribute(xml_pb_type, "mode_bits", loc_data, pugiutil::ReqOpt::OPTIONAL).as_string());
+  pb_type_annotation.set_mode_bits(mode_bit_data);
 
   /* If this is a physical pb_type, circuit model name is an optional attribute, 
    * which is applicable to leaf pb_type in the hierarchy 
diff --git a/libopenfpga/libarchopenfpga/src/write_xml_pb_type_annotation.cpp b/libopenfpga/libarchopenfpga/src/write_xml_pb_type_annotation.cpp
index a771c782d..531e117f1 100644
--- a/libopenfpga/libarchopenfpga/src/write_xml_pb_type_annotation.cpp
+++ b/libopenfpga/libarchopenfpga/src/write_xml_pb_type_annotation.cpp
@@ -159,7 +159,12 @@ void write_xml_pb_type_annotation(std::fstream& fp,
 
   /* Output mode_bits */
   if (!pb_type_annotation.mode_bits().empty()) { 
-    write_xml_attribute(fp, "mode_bits", pb_type_annotation.mode_bits().c_str());
+    /* Convert the vector of integer to string */
+    std::string mode_bits_str;
+    for (const size_t& bit : pb_type_annotation.mode_bits()) {
+      mode_bits_str += std::to_string(bit);
+    }
+    write_xml_attribute(fp, "mode_bits", mode_bits_str.c_str());
   }
 
   /* Output circuit model name */