diff --git a/src/src.ino b/src/src.ino
index 55c4216..cb8d898 100644
--- a/src/src.ino
+++ b/src/src.ino
@@ -48,7 +48,7 @@ void processCommand() {
 
 	if (current_arg.equals("*IDN?")) {
 		// CMD: *IDN?
-		Serial.print("SourceBots:Arduino:X:2.0\n");
+		Serial.print("SourceBots:Arduino:X:2.1\n");
 		return;
 	}
 
@@ -125,6 +125,16 @@ void processCommand() {
 			}
 			else if (current_arg.equals("SET")) {
 				getSlice();
+				// Check if the pin is in the correct mode
+				int mode = getPinMode(pin);
+				if (mode != OUTPUT) {
+					if (mode == INPUT) {
+						Serial.print("NACK:Digital write is not supported in INPUT\n");
+					} else {
+						Serial.print("NACK:Digital write is not supported in INPUT_PULLUP\n");
+					}
+					return;
+				}
 				if (current_arg.equals("1")) {
 					// CMD: PIN:<n>:DIGITAL:SET:1
 					digitalWrite(pin, HIGH);
@@ -144,6 +154,16 @@ void processCommand() {
 			getSlice();
 			if (current_arg.equals("GET?")) {
 				// CMD: PIN:<n>:ANALOG:GET?
+				// Check if the pin is in the correct mode
+				int mode = getPinMode(pin);
+				if (mode != INPUT) {
+					if (mode == OUTPUT) {
+						Serial.print("NACK:Analog read is not supported in OUTPUT\n");
+					} else {
+						Serial.print("NACK:Analog read is not supported in INPUT_PULLUP\n");
+					}
+					return;
+				}
 				Serial.print(analogRead(pin));
 				Serial.print("\n");
 				return;