diff --git a/common/adc_value.h b/common/adc_value.h
index 3edb80d..5ae05f8 100644
--- a/common/adc_value.h
+++ b/common/adc_value.h
@@ -47,7 +47,7 @@ namespace adc
 struct AdcValueHolderErrorCategory : public std::error_category {
     AdcValueHolderErrorCategory() : std::error_category() {}
 
-    const char* name() const noexcept { return "ADC_VALUEHOLDER_CATEGORY"; }
+    const char* name() const noexcept { return "ADC_VALUE_HOLDER_CATEGORY"; }
 
     std::string message(int ec) const
     {
@@ -273,7 +273,7 @@ public:
 
 
     template <typename UT>
-    operator UT()
+    operator UT() const
     {
         // using v_t = std::remove_reference_t<UT>;
         // using val_t = std::conditional_t<std::is_array_v<v_t>, std::add_pointer_t<std::remove_extent_t<v_t>>, v_t>;
@@ -422,6 +422,8 @@ public:
         AdcValueHolder::setupTrivialConvertFunc<VALT, std::decay_t<decltype(tpl)>>();
     }
 
+    AdcSerializingValueHolder(const AdcSerializingValueHolder&) = default;
+    AdcSerializingValueHolder(AdcSerializingValueHolder&&) = default;
 
     virtual ~AdcSerializingValueHolder() = default;
 
@@ -474,7 +476,24 @@ public:
 
     void deserialize(const SerializedT& sval) { _deserializerWrapper(sval); }
 
-    using AdcValueHolder::operator=;
+    AdcSerializingValueHolder& operator=(const AdcSerializingValueHolder&) = default;
+    AdcSerializingValueHolder& operator=(AdcSerializingValueHolder&&) = default;
+
+    template <typename UT>
+    AdcSerializingValueHolder& operator=(UT&& value)
+    {
+        AdcValueHolder::operator=(std::forward<UT>(value));
+
+        return *this;
+    }
+
+    // using AdcValueHolder::operator=;
+
+    // template <typename UT>
+    // operator UT()
+    // {
+    //     return AdcValueHolder::operator UT();
+    // }
 };
 
 
diff --git a/device/adc_device_attribute.h b/device/adc_device_attribute.h
index 4fdd8c2..8a1ae45 100644
--- a/device/adc_device_attribute.h
+++ b/device/adc_device_attribute.h
@@ -13,10 +13,68 @@
 namespace adc
 {
 
-template <typename IdentT, typename SerializedT = std::string>
-class AdcDeviceAttribute : public AdcSerializingValueHolder<SerializedT>
+// error codes
+enum class AdcDeviceAttributeErrorCode : int { ERROR_OK, ERROR_READ_ONLY, ERROR_WRITE_ONLY };
+
+}  // namespace adc
+
+
+namespace std
 {
-    using base_t = AdcSerializingValueHolder<SerializedT>;
+
+template <>
+class is_error_code_enum<adc::AdcDeviceAttributeErrorCode> : public true_type
+{
+};
+
+}  // namespace std
+
+
+
+namespace adc
+{
+
+// error category
+struct AdcDeviceAttributeErrorCategory : public std::error_category {
+    AdcDeviceAttributeErrorCategory() : std::error_category() {}
+
+    const char* name() const noexcept { return "ADC_DEVICE_ATTRIBUTE_CATEGORY"; }
+
+    std::string message(int ec) const
+    {
+        AdcDeviceAttributeErrorCode err = static_cast<AdcDeviceAttributeErrorCode>(ec);
+
+        switch (err) {
+            case AdcDeviceAttributeErrorCode::ERROR_OK:
+                return "OK";
+            case AdcDeviceAttributeErrorCode::ERROR_READ_ONLY:
+                return "device attribute is read-only";
+            case AdcDeviceAttributeErrorCode::ERROR_WRITE_ONLY:
+                return "device attribute is write-only";
+            default:
+                return "UNKNOWN";
+        }
+    }
+
+    static const AdcDeviceAttributeErrorCategory& get()
+    {
+        static const AdcDeviceAttributeErrorCategory constInst;
+        return constInst;
+    }
+};
+
+
+inline std::error_code make_error_code(AdcDeviceAttributeErrorCode ec)
+{
+    return std::error_code(static_cast<int>(ec), AdcDeviceAttributeErrorCategory::get());
+}
+
+
+
+template <typename IdentT, typename SerializedT = std::string>
+class AdcDeviceAttribute : protected AdcSerializingValueHolder<SerializedT>
+{
+    typedef AdcSerializingValueHolder<SerializedT> base_t;
 
     template <typename T>
     using ret_value_t = base_t::template ret_value_t<T>;
@@ -142,6 +200,9 @@ public:
     }
 
 
+    AdcDeviceAttribute(const AdcDeviceAttribute&) = default;
+    AdcDeviceAttribute(AdcDeviceAttribute&&) = default;
+
 
     virtual ~AdcDeviceAttribute() = default;
 
@@ -149,7 +210,31 @@ public:
 
     AccessType accessType() const { return _accessType; }
 
-    using base_t::operator=;
+    template <typename UT>
+    operator UT() const
+    {
+        if (_accessType == WriteOnly) {
+            throw std::system_error(AdcDeviceAttributeErrorCode::ERROR_WRITE_ONLY);
+        }
+
+        return base_t::operator UT();
+    }
+
+    AdcDeviceAttribute& operator=(const AdcDeviceAttribute&) = default;
+    AdcDeviceAttribute& operator=(AdcDeviceAttribute&&) = default;
+
+    template <typename UT>
+    AdcDeviceAttribute& operator=(UT&& value)
+    {
+        if (_accessType == ReadOnly) {
+            throw std::system_error(AdcDeviceAttributeErrorCode::ERROR_READ_ONLY);
+        }
+
+        base_t::operator=(std::forward<UT>(value));
+
+        return *this;
+    }
+
 
 protected:
     IdentT _ident;