using Serialx (Serial1, Serial2, Serial3) connected to PC produces Garbage

Using Arduino Project Guidance
#1

I am attempting to communicate with my PC using one of the Serialx (Serial1, Serial2, Serial3) ports with very little success. The output on the PC is garbage.

I have tested both Serial1 and Serial3 with the same problems. I have atmega2560 and using a “USB to serial” cable converter. Following is my sketch:

void setup() {
Serial1.begin(9600);
}
void loop(){
// repeat writing “abc” 3 times
for(int i=0;i<3;i++) {
Serial1.write(61);
Serial1.write(62);
Serial1.write(63);
}

delay(200);
}

the output displayed in hex:

61 B0 60 61 B0 60 61 B0 60

Notice the only letter that is correct is the first one, the letter little ‘a’.
I have also tried Serial1.print() which produces the same results.
I have tried various Windows Device Manager and Putty port configuration settings. Different settings create different results, all incorrect. The test above is using 9600/8/N/1 and Flow Control: NONE

I am creating the hex view by cut/paste from the Putty terminal/window into a binary editor (MS Visual Studio).

Questions:

  1. Has anyone successfully communicated with the PC using the Serialx ports?
  2. What should the Windows Device Manager and Putty port settings be?
  3. Can you control/set the prort settings in the Arduino sketch, and if so, how?

thanks, JL

#2

How are you doing the serial level conversion and inversion before connecting to the USB device?

#3

AWOL: don't understand what you mean by "...doing the serial level conversion and inversion before connecting to the USB device?..."

thanks for your quick response.

#4

the output displayed in hex:

Which version of the IDE are you using V1.0?

61 (decimal) is not the lower case letter 'a'. It is the equals sign '='. 62 is > and 63 is ? If you want lower case a, b and c you need to use 0x61, 0x62 and 0x63.

Pete

#5

I am using Arduino 1.0 IDE.

You are correct about the character values. I have tried the (decimal) values 97, 98 and 99 as well as 0x61, 0x62 and 0x63 which produce the following hex values on the PC:

4F A7 4E.....repeated forever

As you pointed out, when sending the (decimal) values 61, 62 and 62, I should have received =>? which are the hex values: 0x3D, 0x3E and 0x3F, but as you can see, I did not get these values.

#6

You cannot simply connect TTL level serial lines to an RS232 serial converter and expect sensible results. a) The signals are inverted b) the signals are level-shifted.

You need something like a MAX232 to do the conversion for you.

#7

thank you AWOL. if I am understanding you correctly, I will need the following:

  1. from the atmega2560 board, I would connect the TX/TX/GND ports to a TTL converter (like the MAX232)
  2. the MAX232 would be connected to my USB-to-RS232 cable converter
  3. the USB-to-RS232 cable converter would plug into my PC in a USB port.

or, are there devices that convert the TTL signals to USB directly?

#8

On the parallax site they have a schematic of a simple RX/TX adapter to go to /from TTL to RS232 I built one for programming my basic stamp.

#9

What is the spec on your "USB to serial" cable converter? It's likely that the cable already has the electronics for the level conversion built into it.

#10

jlb1: or, are there devices that convert the TTL signals to USB directly?

Arduino clones that don't include a USB port are usually programmed via the SPI, aren't they? There is a common interface you can get that connects to the SPI and provides a USB interface. Perhaps you could use one of these instead of going via RS232?

#11