Cisco Switch not receiving serial communication from Arduino So I have an issue that I can't really think of a reason why it would be happening. I have an Arduino Mega connected on Serial3 to a RS232 breakout board with a male DB9 connector on it. I then have two female breakout boards connected. One is connected to the RS232 breakout board and the other to a Cisco DB9 to roll over cable, which is connected to my Cisco Switch, or if it is, it is being ignored.

For some reason no data sent from the Arduino is making it to the Cisco switch that I can tell. I did confirm that it is sending data using a USB to DB9 adapter and PUTTY. I can send and receive data from both the Arduino and PUTTY correctly to the other.

I can receive data from the switch perfectly. Cisco's default settings are the same as the Arduino's, 9600, 8bits, no parity, 1 stop bit etc...

I can also connect the switch to the USB to DB9 adapter directly and send and receive fine through it / PUTTY as well.

Does anyone have any suggestions why I'd be able to send data to and from Putty, but only receive data from the switch, or why the data going to the switch is failing?



void setup() {
  Serial.begin(9600, SERIAL_8N1);
  Serial3.begin(9600, SERIAL_8N1);
  Serial.println("Ready....");
  Serial.println();
}

void loop() {
  // read from Serial3, write to Serial
  if (Serial3.available()) {
    int inByte = Serial3.read();
    Serial.write(inByte);
  }
  // read from Serial, write to Serial3
  if (Serial.available()) {
    int inByte = Serial.read();
    Serial3.write(inByte);
  }
  Serial3.println(); // Added just to test if a cr could be passed
  Serial3.write(98); // Added just to test if a character could be directory passed
  Serial3.write(10); // Added just to test if a cr could be passed
}
Assuming this is a flow control problem:


  Is there such a thing as inb vs oob for a serial console connection?
  This isn't on the internal network of the switch in any way but the
  console port


It assumed this is a managed switch and the traffic on the console port has nothing to do with the traffic going through the switch. Rather this is likely a port to the computer inside the switch.  Such a port might be able to use RTS/CTS/DSR or X-on / and X-off. 

If this is a flow control problem, consider first looking for thumb switches on the back of the switch to see if the method used for flow control over the console port can be selected. If that is not possible, consider simply hardwiring the out of band flow control pins to always allow for data to flow.  At 9600 baud, a dedicated Aruidno should be able to keep up.

Refer to the 9 pin connector in this chart to find the out of band flow control pins.