// (c) Michael Schoeffler 2018, http://www.mschoeffler.de
#include <SoftwareSerial.h>
const int BUFFER_SIZE = 14; // RFID DATA FRAME FORMAT: 1byte head (value: 2), 10byte data (2byte version + 8byte tag), 2byte checksum, 1byte tail (value: 3)
const int DATA_SIZE = 10; // 10byte data (2byte version + 8byte tag)
const int DATA_VERSION_SIZE = 2; // 2byte version (actual meaning of these two bytes may vary)
const int DATA_TAG_SIZE = 8; // 8byte tag
const int CHECKSUM_SIZE = 2; // 2byte checksum
SoftwareSerial ssrfid = SoftwareSerial(6,8);
uint8_t buffer[BUFFER_SIZE]; // used to store an incoming data frame //// almacena la cadena
int buffer_index = 0; // puntero
void setup() {
Serial.begin(9600);
ssrfid.begin(9600); // inicio comunicacion
ssrfid.listen(); // selecciono este serial
Serial.println("INIT DONE"); //veo que transmita
}
void loop() {
if (ssrfid.available() > 0)// si el puerto esta recibiendo
{
bool call_extract_tag = false; // bandera
int ssvalue = ssrfid.read(); // read // almaceno el dato entrante en ssvalue
if (ssvalue == -1) { // no data was read
return;
}
if (ssvalue == 2) { // RDM630/RDM6300 found a tag => tag incoming // tag encontrado
buffer_index = 0; // coloco puntero en posicion 0
} else if (ssvalue == 3) { // tag has been fully transmitted // si llega el 3 ya leyo los 14bits
call_extract_tag = true; // extract tag at the end of the function call // llamo la funcion para extraer el tag
}
if (buffer_index >= BUFFER_SIZE) { // checking for a buffer overflow (It's very unlikely that an buffer overflow comes up!)poco probable que se desborde el buffer
Serial.println("Error: Buffer overflow detected!");
return;
}
//Serial.println(buffer_index);
buffer[buffer_index++] = ssvalue; // everything is alright => copy current value to buffer // coloco dato en el buffer [0] incremento puntero
if (call_extract_tag == true)
{
if (buffer_index == BUFFER_SIZE) {
unsigned tag = extract_tag();
} else { // something is wrong... start again looking for preamble (value: 2)
buffer_index = 0;
return;
}
}
}
}
unsigned extract_tag() {
uint8_t msg_head = buffer[0];
uint8_t *msg_data = buffer + 1; // 10 byte => data contains 2byte version + 8byte tag
uint8_t *msg_data_version = msg_data;
uint8_t *msg_data_tag = msg_data + 2;
uint8_t *msg_checksum = buffer + 11; // 2 byte
uint8_t msg_tail = buffer[13];
// print message that was sent from RDM630/RDM6300
Serial.println("--------");
Serial.print("Message-Head: ");
Serial.println(msg_head);
Serial.println("Message-Data (HEX): ");
for (int i = 0; i < DATA_VERSION_SIZE; ++i) {
Serial.print(char(msg_data_version[i]));
}
Serial.println(" (version)");
for (int i = 0; i < DATA_TAG_SIZE; ++i) {
Serial.print(char(msg_data_tag[i]));
}
Serial.println(" (tag)");
Serial.print("Message-Checksum (HEX): ");
for (int i = 0; i < CHECKSUM_SIZE; ++i) {
Serial.print(char(msg_checksum[i]));
}
Serial.println("");
Serial.print("Message-Tail: ");
Serial.println(msg_tail);
Serial.println("--");
long tag = hexstr_to_value(msg_data_tag, DATA_TAG_SIZE);
Serial.print("Extracted Tag: ");
Serial.println(tag);
long checksum = 0;
for (int i = 0; i < DATA_SIZE; i+= CHECKSUM_SIZE) {
long val = hexstr_to_value(msg_data + i, CHECKSUM_SIZE);
checksum ^= val;
}
Serial.print("Extracted Checksum (HEX): ");
Serial.print(checksum, HEX);
if (checksum == hexstr_to_value(msg_checksum, CHECKSUM_SIZE)) { // compare calculated checksum to retrieved checksum
Serial.print(" (OK)"); // calculated checksum corresponds to transmitted checksum!
} else {
Serial.print(" (NOT OK)"); // checksums do not match
}
Serial.println("");
Serial.println("--------");
return tag;
}
long hexstr_to_value(char *str, unsigned int length) { // converts a hexadecimal value (encoded as ASCII string) to a numeric value
char* copy
= malloc((sizeof(char) * length
) + 1); memcpy(copy
, str
, sizeof(char) * length
); copy[length] = '\0';
// the variable "copy" is a copy of the parameter "str". "copy" has an additional '\0' element to make sure that "str" is null-terminated.
long value
= strtol(copy
, NULL
, 16); // strtol converts a null-terminated string to a long value return value;
}
