#define LED 21
hw_timer_t *Mi_timer = NULL;


void IRAM_ATTR onTimer(){
    digitalWrite(LED, !digitalRead(LED));
}
void setup() {
pinMode(LED, OUTPUT);
Mi_timer = timerBegin(0, 80, true);             //Definir numero del timer, preescalar, ascendente
timerAttachInterrupt(Mi_timer, &onTimer, true); //Vincular y habilitar temporizador
timerAlarmWrite(Mi_timer, 200000, true);        //200000us
timerAlarmEnable(Mi_timer);                     //Just Enable
}
void loop() {
}