String retazec = "M:4 P:1:4 R:0 F:0 U:300 50Hz 25C 295V 0mA 0W 67us 0Wh";
const char terminator[2] = " "; //medzera
void setup() {
  Serial.begin(115200);
  parsuj(retazec);
}

void loop() {

}

void parsuj(String vstup) {
  char pole_znakov[vstup.length() + 1];
  vstup.toCharArray(pole_znakov, vstup.length() + 1);
  char *polozka;
  polozka = strtok(pole_znakov, terminator);
  while ( polozka != NULL ) {
    Serial.println(polozka);
    polozka = strtok(NULL, terminator);