Serial via Digital Pins 0 and 1 instead of FTDI

Projects Interfacing w/ Software on the Computer
1

Hello. I have an Arduino Ethernet Board (http://www.arduino.cc/en/Main/ArduinoBoardEthernet). I programmed the board with the following:

void setup()
{
    Serial.begin(115200);
}

void loop()
{
    Serial.print('A');
    delay(5000);
}

This program works great if I use the serial port of the FTDI cable. However, if I connect the Arduino's digital pins 0 and 1 to another serial cable's TX and RX lines respectively, and use that serial cable instead of the FTDI cable, I get garbage on the other side (to be exact, 0x00 and a BREAK condition). I can't find any documentation regarding this. Do I need to also apply a common ground of some sort? I would greatly appreciate any help!

2

Do I need to also apply a common ground of some sort?

Of course. Electrons need a way to get back, in order to make current flow, in order to toggle the bits.

3

You need to connect an RS232 to TTL converter, if you are using other serial ports. This changes the voltage levels and inverts the signals.

4

FYI, I'm referring to Serial (RS232) modem cable (DB9-DB15). Pinout and signals for building a serial (RS232) modem cable, and I'm using a DB9 connector.

PaulS, thank you. Referring to the pinouts on the above link, I hooked the Arduino's GND (right below the 5V) to pin 5, and it changed nothing.

Of course, if Grumpy_Mike is correct, then it changing nothing makes sense. Grumps, to make sure I understand: TTL is coming from the Arduino pins 0 and 1, and it needs to be converted to RS232. Correct?

5

TTL is coming from the Arduino pins 0 and 1

Yes.

it needs to be converted to RS232

If you are trying to connect it to another RS232 device then yes.

However if you are connecting it to a device that needs TTL signals then no.

But - that cable is used to connect to RS232 signals, if the device you are trying to talk to has a DB9 connector on it then it will be RS232.

6

Perfect. I'm set, thank you both!