// Serial write example
// https://arduino.stackexchange.com/questions/90195/send-hex-number-over-serial

void setup() {
  Serial.begin(115200);

  Serial1.begin(115200); // Serial1 is connected to the custom chip

  const size_t packet_length = 6;
  uint8_t packet[packet_length] = {0xaa, 0xbb, 0x03, 0x01, 0x03, 0xee};
  Serial1.write(packet, packet_length);
}

void loop() {
  while (Serial1.available()) {
    //Serial.print((char)Serial1.read()); // ascii 'ª»î' which is AA BB 03 01 03 EE in hex (which is a match)
    Serial.print(Serial1.read()); // decimal '170 187 3 1 3 238'

  }
}

uart-chip-example.ino

diagram.json

// Wokwi Custom UART Chip Example
//
// This chip implements a simple ROT13 letter substitution cipher.
// It receives a string over UART, and returns the same string with
// each alphabetic character replaced with its ROT13 substitution.
//
// For information and examples see:
// https://link.wokwi.com/custom-chips-alpha
//
// SPDX-License-Identifier: MIT
// Copyright (C) 2022 Uri Shaked / wokwi.com

#include "wokwi-api.h"
#include <stdio.h>
#include <stdlib.h>

DEFINE_PIN(RX);
DEFINE_PIN(TX);
DEFINE_PIN(VCC);
DEFINE_PIN(GND);

typedef struct {
  uart_dev_t uart0;
} chip_state_t;

static void on_uart_rx_data(void *ctx, uint8_t byte);
static void on_uart_write_done(void *ctx);

void* chip_init(void) {
  setvbuf(stdout, NULL, _IOLBF, 1024); // Disable buffering for debug logs

  chip_state_t *chip = malloc(sizeof(chip_state_t));

  const uart_config_t uart_config = {
    .tx = pin_init("TX", INPUT_PULLUP),
    .rx = pin_init("RX", INPUT),
    .baud_rate = 115200,
    .rx_data = on_uart_rx_data,
    .write_done = on_uart_write_done,
  };
  chip->uart0 = uart_init(chip, &uart_config);

  printf("UART Chip initialized!\n");

  return chip;
}

static uint8_t rot13(uint8_t value) {
  const uint8_t ROT = 13;

  // Comment out these lines to turn the rot13 into a simple unmodified echo
  // if(value >= 'A' && value <='Z') {
  //   return (value + ROT) <= 'Z' ? value + ROT : value - ROT;
  // }
  // if(value >= 'a' && value <= 'z') {
  //   return (value + ROT) <= 'z' ? value + ROT : value - ROT;
  // }
  return value;
}

 static void on_uart_rx_data(void *ctx, uint8_t byte) {
  chip_state_t *chip = (chip_state_t*)ctx;
  printf("Incoming UART data: %d\n", byte);
  uint8_t data_out = rot13(byte);
  uart_write(chip->uart0, &data_out, sizeof(data_out));
}

static void on_uart_write_done(void *ctx) {
  chip_state_t *chip = (chip_state_t*)ctx;
  printf("UART done\n");
}
