Improve Zonestar keypad responsiveness (#14056)

Marlin/src/lcd/ultralcd.cpp

 
   uint8_t get_ADC_keyValue(void) {
     if (thermalManager.ADCKey_count >= 16) {
-      const uint16_t currentkpADCValue = thermalManager.current_ADCKey_raw >> 2;
-      thermalManager.current_ADCKey_raw = 0;
+      const uint16_t currentkpADCValue = thermalManager.current_ADCKey_raw << 2;
+      thermalManager.current_ADCKey_raw = 1024;
       thermalManager.ADCKey_count = 0;
       if (currentkpADCValue < 4000)
         for (uint8_t i = 0; i < ADC_KEY_NUM; i++) {

Marlin/src/module/temperature.cpp

 // public:
 
 #if HAS_ADC_BUTTONS
-  uint32_t Temperature::current_ADCKey_raw = 0;
+  uint32_t Temperature::current_ADCKey_raw = 1024;
   uint8_t Temperature::ADCKey_count = 0;
 #endif
 
 
   #if HAS_ADC_BUTTONS
     static unsigned int raw_ADCKey_value = 0;
+    static bool ADCKey_pressed = false;
   #endif
 
   #if ENABLED(SLOW_PWM_HEATERS)
           next_sensor_state = adc_sensor_state; // redo this state
         else if (ADCKey_count < 16) {
           raw_ADCKey_value = HAL_READ_ADC();
-          if (raw_ADCKey_value > 900) {
-            //ADC Key release
-            ADCKey_count = 0;
-            current_ADCKey_raw = 0;
-          }
-          else {
-            current_ADCKey_raw += raw_ADCKey_value;
+          if (raw_ADCKey_value <= 900) {
+            NOMORE(current_ADCKey_raw, raw_ADCKey_value);
             ADCKey_count++;
           }
+          else { //ADC Key release
+            if (ADCKey_count > 0) ADCKey_count++; else ADCKey_pressed = false;
+            if (ADCKey_pressed) {
+              ADCKey_count = 0;
+              current_ADCKey_raw = 1024;
+            }
+          }
         }
+        if (ADCKey_count == 16) ADCKey_pressed = true;
         break;
     #endif // ADC_KEYPAD