Serial 3 vs Software Serial

Question

So I have a program that works great on the Mega, it uses serial 3 to read and streams out to the USB (I posted a previous question which someone answered) I tried to use Serial (D0) to read and then write to serial, which did not work. So now I am looking in to Software Serials

Is there a difference between a real serial and software serial as it does not seem to be working, It all runs a bit slower

#include <SoftwareSerial.h>
const int DesiredRPM=300; // Setting Desired RPM Here.
const int MotorPWMPin=4;
int inByte = 0; // incoming serial byte
unsigned char Data_status=0;
unsigned char Data_4deg_index=0;
unsigned char Data_loop_index=0;
unsigned char SpeedRPHhighbyte=0; // 
unsigned char SpeedRPHLowbyte=0;
int SpeedRPH=0;
const unsigned char PWM4dutyMax=255;
const unsigned char PWM4dutyMin=100;
unsigned char PWM4duty=PWM4dutyMin; // have to set a default value make motor start spining
SoftwareSerial mySerial(10, 11); // RX, TX
void setup() {
 pinMode(MotorPWMPin, OUTPUT); 
 Serial.begin(115200); // USB serial
 Serial3.begin(115200); // XV-11 LDS data 
 // prints title with ending line break 
 Serial.println("Arduino Neato XV-11 Motor control board v0.1 by Cheng-Lung Lee"); 
 // Pick your magic number and drive your motor , 178 is 178/255*5V=3.49V
 analogWrite(MotorPWMPin, PWM4duty ); 
 mySerial.begin(115200);
}
void loop() {
 // if we get a valid byte from LDS, read it and send it to USB-serial
 if (Serial3.available() > 0) {
 // get incoming byte:
 inByte = Serial3.read();
 //Serial.print(inByte, BYTE);
 //Serial.write(inByte);
 Serial.print((char)inByte);
 decodeData(inByte);
 }
 if (mySerial.available() > 0) {
 // get incoming byte:
 inByte = mySerial.read();
 //Serial.print(inByte, BYTE);
 //Serial.write(inByte);
 Serial.print((char)inByte);
 decodeData(inByte);
 }
}
void decodeData(unsigned char inByte){
 switch (Data_status){
 case 0: // no header
 if (inByte==0xFA)
 {
 Data_status=1;
 Data_loop_index=1;
 }
 break;
 case 1: // Find 2nd FA
 if (Data_loop_index==22){
 if (inByte==0xFA)
 {
 Data_status=2;
 Data_loop_index=1;
 } 
 else // if not FA search again
 Data_status=0;
 }
 else{
 Data_loop_index++;
 }
 break;
 case 2: // Read data out
 if (Data_loop_index==22){
 if (inByte==0xFA)
 {
 Data_loop_index=1;
 } 
 else // if not FA search again
 Data_status=0;
 }
 else{
 readData(inByte);
 Data_loop_index++;
 }
 break;
 }
}
void readData(unsigned char inByte){
 switch (Data_loop_index){
 case 1: // 4 degree index
 Data_4deg_index=inByte-0xA0;
// Serial.print(Data_4deg_index, HEX); 
// Serial.print(": "); 
 break;
 case 2: // Speed in RPH low byte
 SpeedRPHLowbyte=inByte;
 break;
 case 3: // Speed in RPH high byte
 SpeedRPHhighbyte=inByte;
 SpeedRPH=(SpeedRPHhighbyte<<8)|SpeedRPHLowbyte;
 SpeedControl ( DesiredRPM ) ; // 
// Serial.print(SpeedRPHhighbyte, HEX); 
// Serial.println(SpeedRPHLowbyte, HEX); 
 break;
 default: // others do checksum
 break;
 } 
}
// Very simple speed control
void SpeedControl ( int RPMinput)
{
 if (Data_4deg_index%30==0) { // I only do 3 updat I feel it is good enough for now
 if (SpeedRPH<RPMinput*60)
 if (PWM4duty<PWM4dutyMax) PWM4duty++; // limit the max PWM make sure it don't overflow and make LDS stop working
 if (SpeedRPH>RPMinput*60)
 if(PWM4duty>PWM4dutyMin) PWM4duty--; //Have to limit the lowest pwm keep motor running
 } 
 analogWrite(MotorPWMPin, PWM4duty ); // update value
}

Answer 1

There are huge differences. The most important ones are:

• SoftwareSerial is half duplex (it can send or it can receive, it cannot do both at once)
• SoftwareSerial is blocking - while it is sending or receiving nothing else can happen

SoftwareSerial is very much a poor-man's serial port. It should only really be used for very low volume data (things like NEMA messages once a second or so) and only if you have absolutely no choice (and, let's face it, you always have a choice).

• Burf2000: Ok thank you, damn I need 2 serial ports then. I read on the serial and send on to USB.
• Majenko: That is often the case. That is why Atmel came up with the "upgrade" of the ATMega328PB which has a second UART. Another good choice is the ATMega32U4 (as used on the Leonardo) which separates the USB from the UART so you can use both separately.
• Burf2000: Oh brilliant, I only need it for this project, so I should get a Leonardo, hopefully it's smaller than the mega
• Majenko: It's the same footprint as the Uno.
• Burf2000: Thanks you :) out of scope I know but any down point? Like not compatible with shield etc. Assuming the Leonardo uses serial1