Multiple serial connections

Projects General Guidance
1

I plan on having two serial devices connected to an arduino. I am not sure whether to use the uno or mega. I am writing a program for autonomous navigation. It will use one of the serial ports to receive gps information and calculate its course based on that, but I want to be able to override that with manual commands from a computer via an xbee (the other serial connection).

Is it possible just to use softserail and monitor it for a command?

2

LittleDice:
Is it possible just to use softserail and monitor it for a command?

Yes, although you'd be better off putting the GPS on the software UART - missing or misinterpreting user commands is more risky than corrupting a single packet of GPS data.

3

Could you give me some sudo code that would check to see if there are any commands being received?

4 
while (Serial.available()) {
 // process serial byte by byte
  char c = Serial.read();
}
5

It's my understanding, that command does not work when you use the softserial library.

6

Using NewSoftSerial for software UART:

#include <NewSoftSerial.h>
NewSoftSerial nss(rx, tx);
 // [...]
while (nss.available()) {
  char c = nss.read();
}

Don't use the default SoftwareSerial class - it's inefficient in comparison to NewSoftSerial, and its only advantage is that it's included with the IDE.

7

Ok I must be reading this wrong then. Here is a code snippet off there page. NewSoftSerial | Arduiniana

This means that you can’t write code like this:
void loop()
{
  if (device1.available() > 0)
  {
    int c = device1.read();
    ...
  }
  if (device2.available() > 0)
  {
    int c = device2.read();
    ...
  }
}
This code will never do anything but activate one device after the other.
8

That's if you've got more than one software serial port. NSS only supports one port active at a time - each port needs to be set to active when it's being used. However, you can use as many hardware UARTs as you've got avalable + one NSS port without issues.

Please read ALL of the page, as well as ALL of the examples, before pulling something out of context.

This line: "An important point here is that object.available() always returns 0 unless object is already active." is literally right before the one you quoted, but you quite evidently didn't read it. (emphasis mine).

9

I mean no disrespect I am just trying to understand how it works. So basically I can just make a loop and run through it to keep checking if I am overriding it?

10

The *.available() method returns the number of bytes in the buffer. You will need to periodically check if it is non-zero (buffer has bytes to be read), and then process them if they are available.

11

So by using soft serial it won't delete what is in my hardware ports buffer?

12

They use different buffers, so no.