Hardware serial not working, SoftwareSerial is

Question

On my Uno-equivalent Arduino, a SoftwareSerial connection (on RX, TX = 8, 9) is working*, while a hardware serial connection to the same device, set up in the same way (but on pins RX, TX = 0, 1) is not working. Why is the hardware serial setup not working?

*By working I mean receiving a byte from the external device

Edit: as a simple example:

void setup() {
 Serial.begin(38000);
 pinMode(7, OUTPUT);
}
void draw() {
 if (Serial.available() > 0) {
 Serial.read();
 tone(7, 440, 1000);
 }
}

The above, using Serial, doesn't work, whereas

#include <SoftwareSerial.h>
SoftwareSerial serial(8, 9);
void setup() {
 serial.begin(38000);
 pinMode(7, OUTPUT);
}
void draw() {
 if (serial.available() > 0) {
 serial.read();
 tone(7, 440, 1000);
 }
}

does work.

---

I don't know if this helps, but connecting RX/TX through an LED to ground gave me the following, using Serial on (0, 1) and SoftwareSerial on (8, 9):

Serial
RX: bright
TX: bright
SoftwareSerial
RX: dim (but still lit)
TX: bright

Is the fact that RX is dim using SoftwareSerial significant?

• Nick Gammon: Please post your code. Please define "not working". What device have you connected?
• Dodo: @NickGammon This is interfacing with a CASIO fx-9750GII. I can receive the request byte from the calculator using SoftwareSerial but not with Serial. If the Arduino receives any data it makes a sound.
• frarugi87: What if you try SoftwareSerial serial(0,1);?
• James Waldby - jwpat7: 38000 bps is not a standard rate and hardware at one end or the other might not support it, while software might not care. You still haven't said what "doesn't work" means, but if it means garbled characters, use a standard rate, eg 38400 bps.
• Dodo: @jwpat7 'Doesn't work' means no byte is received. The external device supports 38000 bps only, and the Arduino can use it on the hardware serial port (as tested connected to a computer with a Processing sketch). The fact that it is simultaneously connected to a computer through the USB port doesn't seem to be an issue, because it exhibits the same behaviour powered by a phone charger (unless the charger also interferes with something?).

Answer 1

There may be several reasons

1. Be sure uC pin connect pin header
2. In setup part, you write Serial.begin(xxxx);
3. After serial begin, don't change this pins IO features(Input, output)

Please check that after if not solve, please share code

• Dodo: Can you explain what you mean in 1?
• Nick Gammon: Also explain what you mean by (3).
• Dodo: I think that means don't use pinMode on pins 0 or 1.
• Majenko: I think a translation might be: 1. Make sure you connect to the right pins. 2. Be sure to use Serial.begin(baud). 3. Never use pinMode() on pins 0 and 1 when you are using Serial.
• Dodo: In that case: check, check and check... I think.

Answer 2

I would check if the arduino you are using supports your selected baudrate.

38000 is not a standard rate and it could be, that the hardware is not able to work at it with the needed precision. The software serial (and most USB serial dongles) could use any baudrate, but not the limited hardware within most arduinos.