I am trying use a HMI display. If I want to send a data, for example I want to write "TOPWAY" to 0x00000080 address it should like that:

    Serial.write(0xaa); // packet head
    Serial.write(0x42); // VP_N16 string write command
    Serial.write(0x00); // VP_N16 address
    Serial.write(0x54); //T
    Serial.write(0x4f); //O
    Serial.write(0x50); //P
    Serial.write(0x57); //W
    Serial.write(0x41); //A
    Serial.write(0x59); //Y
    Serial.write(0x00); //string end with "\0" 
    Serial.write(0xcc); // packet tail
    Serial.write(0x33); // packet tail
    Serial.write(0xc3); // packet tail
    Serial.write(0x3c); // packet tail

I want to make a method like SendString(String abc) to send that like above. I need convert string a hex array and call in Serial.write(array[i]). Can you hep me?

  • 2
    There is no such thing as a hex array. Everything is all just numbers. Even letters are numbers. Your string is already an array.
    – Majenko
    Jul 28, 2021 at 7:30
  • 2
    Serial.print("TOPWAY"); should do it
    – Juraj
    Jul 28, 2021 at 8:18
  • @Juraj you mean like that for total query like above: Serial.write(0xaa); Serial.write(0x42); Serial.write(0x00); Serial.write(0x00); Serial.write(0x00); Serial.write(0x80); Serial.print("TOPWAY"); Serial.write(0x00); //string end with "\0" Serial.write(0xcc); Serial.write(0x33); Serial.write(0xc3); Serial.write(0x3c); . if Not? please show me as answer not in comment.
    – mehmet
    Jul 28, 2021 at 14:37
  • the answer is below
    – Juraj
    Jul 28, 2021 at 14:44

1 Answer 1


I don't know anything about the particular display, but based on the information provided I hope this is at least shows the foundation of one way you could approach a final solution.


  • Incorporated great improvements and a fix from Edgar in the comments.
  • String overload.
  • Display baud rate suggested by mehmet
#define DISPLAY_DEVICE Serial

static uint8_t displayPktStart[] = {
    0xaa, // packet headchar
    0x42, // VP_N16 string write command
    0x00, // VP_N16 address
    0x00, // ...Fill

static uint8_t displayPktEnd[] = {
    0x00, // End of text
    0xcc, // packet tail
    0x33, // packet tail
    0xc3, // packet tail
    0x3c // packet tail

void writeDisplay(const char* text)
  // Write packet headers
  DISPLAY_DEVICE.write(displayPktStart, sizeof displayPktStart);

  // Send text

  // Write packet tail
  DISPLAY_DEVICE.write(displayPktEnd, sizeof displayPktEnd); 

void writeDisplay(const String& text)

void setup()

void loop() 
  String msg = "TOPWAY";

  writeDisplay("Peanuts taste like chicken");
  writeDisplay("No. Seriously");

  • 3
    1. Instead of writing a loop, you can DISPLAY_DEVICE.write(displayPktStart, sizeof displayPktStart);, and likewise for displayPktEnd. 2. You mean DISPLAY_DEVICE.print(text);, not println(). 3. Serial.print() will not send the terminating \0, you may want to add that to displayPktEnd. Jul 28, 2021 at 9:39
  • @EdgarBonet Thanks. Updated. Jul 28, 2021 at 10:04
  • Thanks A lot. I've added DISPLAY_DEVICE.begin(9600); in setup
    – mehmet
    Jul 28, 2021 at 14:51
  • 1
    @mehmet I hope my update matches your expectations. Jul 28, 2021 at 15:29
  • @voidPointer well, I don't want to bother you too much, but I have one more question. if I want to use dynamic address, such as "000080" instead of Serial.write(0x00); Serial.write(0x00); Serial.write(0x80); how to add this method, like writeDisplay(msg, "000080");
    – mehmet
    Jul 28, 2021 at 19:51

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