diff --git a/schema/core.json b/schema/core.json
index bb8d2cc..f89260b 100644
--- a/schema/core.json
+++ b/schema/core.json
@@ -1,5 +1,5 @@
 {
-    "$schema": "https://json-schema.org/draft-07/schema",
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
     "$id": "https://harp-tech.org/draft-03/schema/core.json",
     "type": "object",
     "allOf": [
@@ -7,12 +7,17 @@
             "properties": {
                 "protocolVersion": {
                     "description": "Specifies the version of the device protocol.",
-                    "pattern": "^(0|[1-9]\\d*)\\.(0|[1-9]\\d*)$",
-                    "type": "string"
+                    "$ref": "#/$defs/version"
                 }
             },
             "required": ["protocolVersion"]
         },
         { "$ref": "registers.json" }
-    ]
+    ],
+    "$defs": {
+        "version": {
+            "type": "string",
+            "pattern": "^(0|[1-9]\\d*)\\.(0|[1-9]\\d*)$"
+        }
+    }
 }
\ No newline at end of file
diff --git a/schema/device.json b/schema/device.json
index 2fe833d..9eaee64 100644
--- a/schema/device.json
+++ b/schema/device.json
@@ -1,5 +1,5 @@
 {
-    "$schema": "https://json-schema.org/draft-07/schema",
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
     "$id": "https://harp-tech.org/draft-03/schema/device.json",
     "type": "object",
     "allOf": [
@@ -15,13 +15,19 @@
                 },
                 "firmwareVersion": {
                     "description": "Specifies the version of the device firmware.",
-                    "pattern": "^(0|[1-9]\\d*)\\.(0|[1-9]\\d*)$",
-                    "type": "string"
+                    "$ref": "core.json#/$defs/version"
                 },
                 "hardwareTargets": {
-                    "description": "Specifies the version of the device hardware.",
-                    "pattern": "^(0|[1-9]\\d*)\\.(0|[1-9]\\d*)$",
-                    "type": "string"
+                    "description": "Specifies the version of the hardware targets.",
+                    "oneOf": [
+                        { "$ref": "core.json#/$defs/version" },
+                        {
+                    "type": "array",
+                            "items": { "$ref": "core.json#/$defs/version" },
+                            "uniqueItems": true,
+                            "minItems": 1
+                    }
+                    ]
                 },
                 "registers": {
                     "additionalProperties": {
diff --git a/schema/ios.json b/schema/ios.json
index e47515c..41d9aea 100644
--- a/schema/ios.json
+++ b/schema/ios.json
@@ -1,15 +1,15 @@
 {
-    "$schema": "https://json-schema.org/draft-07/schema",
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
     "$id": "https://harp-tech.org/draft-03/schema/ios.json",
     "type": "object",
     "description": "Specifies the IO pin configuration used to automatically generate firmware.",
     "additionalProperties": {
         "oneOf": [
-            { "$ref": "#/definitions/inputPin" },
-            { "$ref": "#/definitions/outputPin" }
+            { "$ref": "#/$defs/inputPin" },
+            { "$ref": "#/$defs/outputPin" }
         ]
     },
-    "definitions": {
+    "$defs": {
         "portPin": {
             "type": "object",
             "properties": {
@@ -34,7 +34,7 @@
             "required": ["port", "pinNumber", "direction"]
         },
         "inputPin": {
-            "allOf": [{ "$ref": "#/definitions/portPin" }],
+            "allOf": [{ "$ref": "#/$defs/portPin" }],
             "properties": {
                 "direction": {
                     "enum": ["input"]
@@ -62,7 +62,7 @@
             }
         },
         "outputPin": {
-            "allOf": [{ "$ref": "#/definitions/portPin" }],
+            "allOf": [{ "$ref": "#/$defs/portPin" }],
             "properties": {
                 "direction": {
                     "enum": ["output"]
diff --git a/schema/registers.json b/schema/registers.json
index ad1913f..3928485 100644
--- a/schema/registers.json
+++ b/schema/registers.json
@@ -1,26 +1,26 @@
 {
-    "$schema": "https://json-schema.org/draft-07/schema",
+    "$schema": "https://json-schema.org/draft/2019-09/schema",
     "$id": "https://harp-tech.org/draft-03/schema/registers.json",
     "type": "object",
     "properties": {
         "registers": {
             "type": "object",
             "description": "Specifies the collection of registers implementing the device function.",
-            "additionalProperties": { "$ref": "#/definitions/register" }
+            "additionalProperties": { "$ref": "#/$defs/register" }
         },
         "bitMasks": {
             "type": "object",
             "description": "Specifies the collection of masks available to be used with the different registers.",
-            "additionalProperties": { "$ref": "#/definitions/bitMask" }
+            "additionalProperties": { "$ref": "#/$defs/bitMask" }
         },
         "groupMasks": {
             "type": "object",
             "description": "Specifies the collection of group masks available to be used with the different registers.",
-            "additionalProperties": { "$ref": "#/definitions/groupMask" }
+            "additionalProperties": { "$ref": "#/$defs/groupMask" }
         }
     },
     "required": ["registers"],
-    "definitions": {
+    "$defs": {
         "type": {
             "description": "Specifies the type of the register payload.",
             "type": "string",
@@ -60,7 +60,7 @@
                 },
                 "bits": {
                     "type": "object",
-                    "additionalProperties": { "$ref": "#/definitions/maskValue" }
+                    "additionalProperties": { "$ref": "#/$defs/maskValue" }
                 }
             },
             "required": ["bits"]
@@ -75,7 +75,7 @@
                 },
                 "values": {
                     "type": "object",
-                    "additionalProperties": { "$ref": "#/definitions/maskValue" }
+                    "additionalProperties": { "$ref": "#/$defs/maskValue" }
                 }
             },
             "required": ["values"]
@@ -120,12 +120,12 @@
                     "description": "Specifies a summary description of the payload member.",
                     "type": "string"
                 },
-                "minValue": { "$ref": "#/definitions/minValue" },
-                "maxValue": { "$ref": "#/definitions/maxValue" },
-                "defaultValue": { "$ref": "#/definitions/defaultValue" },
-                "maskType": { "$ref": "#/definitions/maskType" },
-                "interfaceType": { "$ref": "#/definitions/interfaceType" },
-                "converter": { "$ref": "#/definitions/converter" }
+                "minValue": { "$ref": "#/$defs/minValue" },
+                "maxValue": { "$ref": "#/$defs/maxValue" },
+                "defaultValue": { "$ref": "#/$defs/defaultValue" },
+                "maskType": { "$ref": "#/$defs/maskType" },
+                "interfaceType": { "$ref": "#/$defs/interfaceType" },
+                "converter": { "$ref": "#/$defs/converter" }
             }
         },
         "register": {
@@ -136,7 +136,7 @@
                     "type": "integer",
                     "maximum": 255
                 },
-                "type": { "$ref": "#/definitions/type" },
+                "type": { "$ref": "#/$defs/type" },
                 "length": {
                     "description": "Specifies the length of the register payload.",
                     "type": "integer",
@@ -145,10 +145,10 @@
                 "access": {
                     "description": "Specifies the expected use of the register.",
                     "oneOf": [
-                        { "$ref": "#/definitions/access" },
+                        { "$ref": "#/$defs/access" },
                         {
                             "type": "array",
-                            "items": { "$ref": "#/definitions/access" },
+                            "items": { "$ref": "#/$defs/access" },
                             "uniqueItems": true,
                             "minItems": 1,
                             "maxItems": 3
@@ -159,10 +159,10 @@
                     "description": "Specifies a summary description of the register function.",
                     "type": "string"
                 },
-                "minValue": { "$ref": "#/definitions/minValue" },
-                "maxValue": { "$ref": "#/definitions/maxValue" },
-                "defaultValue": { "$ref": "#/definitions/defaultValue" },
-                "maskType": { "$ref": "#/definitions/maskType" },
+                "minValue": { "$ref": "#/$defs/minValue" },
+                "maxValue": { "$ref": "#/$defs/maxValue" },
+                "defaultValue": { "$ref": "#/$defs/defaultValue" },
+                "maskType": { "$ref": "#/$defs/maskType" },
                 "visibility": {
                     "description": "Specifies whether the register function is exposed in the high-level interface.",
                     "type": "string",
@@ -174,10 +174,10 @@
                 },
                 "payloadSpec": {
                     "type": "object",
-                    "additionalProperties": { "$ref": "#/definitions/payloadMember" }
+                    "additionalProperties": { "$ref": "#/$defs/payloadMember" }
                 },
-                "interfaceType": { "$ref": "#/definitions/interfaceType" },
-                "converter": { "$ref": "#/definitions/converter" }
+                "interfaceType": { "$ref": "#/$defs/interfaceType" },
+                "converter": { "$ref": "#/$defs/converter" }
             },
             "required": ["address", "access", "type"]
         }