Trouble reading from RS232 device

Troubleshooting
1

I’m trying to troubleshoot an RS232 connection via Serial1 and don’t really know where to start. If I connect to the device via an RS232-USBC converter to my MBP and use screen (screen /dev/xxx 38400), everything works great. However, when I connect a SparkFun RS232-TTL adapter to my photon and try with the code below, I get nothing. Where can I begin to debug?

Code Example

void setup(){
    // set up serial comms over the USB for debugging
    Serial.begin(9600);

    // set up serial1 for RS232 comms
    Serial1.begin(38400);
}

void loop(){
    Serial.println(Serial1.available());
}

Obviously, this shouldn’t accomplish much, but it would be nice to see that there are bytes to read…

2

Have you tried swapping RX/TX?
Do you see any activity on the RX or TX LEDs?

1 Like
3

Yes - tried switching RX/TX, and no, the LED’s don’t ever light up! I’ve got a Logic Analyzer I can bust out, but not sure what that’s going to tell me since it appears nothing is happening…

4

What if you send data from the Photon, does the TX LED then light up?
Also, do you know whether your RS232 device may require flow control?

5

Yes…I do see some lights flash if I send commands from the photon…why wouldn’t it be able to receive data…?

6

Try a simple passthrough app:

void setup(){
    // set up serial comms over the USB for debugging
    Serial.begin(9600);

    // set up serial1 for RS232 comms
    Serial1.begin(38400);
}

void loop() {
	uint8_t byte;

	if (Serial1.available()) {
		byte = Serial1.read();
		Serial.write(byte);
	}
	if (Serial.available()) {
		byte = Serial.read();
		Serial1.write(byte);
	}
}
7

Maybe it's not that the Photon can't receive data, but ...

... in order to actually send data.

8

Ahh didn’t see the flow control part - I will go look that up in the manual. Would the screen command work if it required flow control?

9

If you can disable flow control on the target side, then do that.
Otherwise it depends what kind of flow control is used in order to know how to emulate/circumvent/mimik it.

10

There may also be hardware flow control which would necessitate the use of a null modem adapter or cable.

11

According to the manual (below), there is no flow control. Are there any other things I can check/be aware of?

34%20PM

12

Is there a way to determine whether hardware flow control is enabled? I used a standard Tripp Lite DB9-USBC cable to easily interact with the device from my Macbook Pro…

Any other common things I should look into?