Docklight and Arduino serial communication (sending hex through RS232) - arduino

Question

I have the following code (I'm using Arduino IDE and a NodeMCU with a MAX3232):
#include <SoftwareSerial.h>
SoftwareSerial RS232Serial(D1, D2); // RX | TX
void setup() {
Serial.begin(9600);
while (!Serial);
RS232Serial.begin(9600);
while (!RS232Serial);
}
void loop() {
Serial.println("Sending msg...");
char msg[] = {0x7E, 0x00, 0x78, 0xF0, 0x7E};
RS232Serial.write(msg, sizeof(msg));
Serial.println("Waiting incomming message:");
while(RS232Serial.available() <= 0) {
delay(1);
}
while(RS232Serial.available() > 0) {
Serial.print(RS232Serial.read(), HEX);
}
Serial.println("");
Serial.println("------------ END -----------");
}
I'm using Docklight to test the communication. So far I'm able to receive the HEX that the NodeMCU boards sends first char msg[] = {0x7E, 0x00, 0x78, 0xF0, 0x7E};. But I'm unable to receive the data properly from Docklight.
The HEX I'm trying to send from Docklight is 7E 00 00 70 15 7E. Debugging with serial monitor, sometimes I receive just 7E and sometimes 0FF, never the complete message. Baud rate, start/stop bits and parity are set to default.
What's wrong with my code?

Answer 1

One reason for not working as expected is:
You are processing the answer as soon as one byte has appeared in the receive buffer.
There is a related example in the Docklight Application Note Arduino Serial Communication - check the code listing on page 5. It makes use of the Arduino SerialEvent() function to collect the incoming telegram byte-per-byte. Only after receiving the end of telegram mark (here: a line feed "\n" character), it sets a flag that tells the code in the main loop() to do something with the accumulated data telegram.
The SerialEvent approach used in the Docklight exampleis not a must. You can solve this inside loop() alone, too. But you certainly need to change the
while(RS232Serial.available() <= 0) {
...
while(RS232Serial.available() > 0) {
parts to something that will wait until a full telegram has been received (or a timeout has occurred).
Now what irritates me still is that you write you sometimes receive "0FF" even though you never send it from Docklight. This could indicate still a second problem on the actual RS232 communication, but it's hard to guess without extra information.
But re-working the telegram receiving part as described above should already make things much clearer and then the source of the "0FF" is probably more obvious.

Answer 2

while(RS232Serial.available() <= 0) {
delay(1);
}
You are only waiting for the serial buffer to have at least 1 byte, but you are not guaranteed that your full message (6 bytes) will be present, when you call RS232Serial.available().
You should wait for the serial buffer to accumulate at least 6 bytes, before you try to read them.
while(RS232Serial.available() < 6) {
delay(1);
}
They you can read the full buffer with:
while(RS232Serial.available() > 0) {
Serial.print(RS232Serial.read(), HEX);
}
or only 6 bytes with:
for (int i=0; i<6; i++) {
Serial.print(RS232Serial.read(), HEX);
}
I don't know about your 0FF, but Serial.print(RS232Serial.read(), HEX) doesn't zero pad the hex string and this could actually be 00 0F 0F or 00 FF.
You should print out the bytes with:
byte b = RS232Serial.read();
if (b < 16) Serial.print('0'); // zero pad
Serial.print(b, HEX);
Serial.print(' '); // add space after each byte