         break;
       case 'a':
         setting = SET_AMPLITUDE;
+        break;
+      case 'm':
+        setting = SET_ADC_HALF;
         break;
       case 'o':
         dds.on();

#define DDS_REFCLK_DEFAULT 19200
#define DDS_REFCLK_OFFSET  0
#define DDS_DEBUG_SERIAL


        Serial.println(F("Tone:   t XXXX = XXXX Hz"));
        Serial.println(F("Amp.:   a XXX  = XXX out of 255"));
        Serial.println(F("DDS:    o = On, O = Off"));
        Serial.println(F("Input:  l = Determine received frequency, L = stop"));
        Serial.println(F("ADC:    m XXX = Set ADC midpoint (zero crossing level)"));
        Serial.println(F("ie. a 31 = 32/255 amplitude, r38400 sets 38400Hz refclk"));
        Serial.println("> ");
        break;
