CODEWITHSUNDEEP
serial-portarduino
marv
marv

Reputation: 11

arduino 2 bytes serial.read

I am beginer in programming, and I need some help to read 2 bytes (msb/lsb) that comes after a request (0x01 to msb and 0x02 to lsb) via serial, and then, make an mathematical operation and display on an 2x16 display. I have the functions of my project that use only 1 byte working good. One example:

void funcao4()
{ 
 int MAP;
float MAP1;
delay(600);
lcd.clear();
lcd.setCursor(0,0);
lcd.print("MAP[mmHG]");


Serial.write(0x06);  //request

if (Serial.available() > 0) 
{

MAP = Serial.read() ;   //read
MAP1 = (MAP * 2.8759 + 91); //operation

lcd.setCursor(0,1);
lcd.print(MAP1); //display

}
}

regards.

Upvotes: 1

Views: 11496

Answers (2)

Hans Passant
Hans Passant

Reputation: 942109

if (Serial.available() >= 2) 
{
    MAP = Serial.read() << 8;
    MAP |= Serial.read();
}

Upvotes: 1

user2461391
user2461391

Reputation: 1433

Wait until the Serial buffer has two bytes, then read them:

void funcao4()
{ 
 int MAP;
float MAP1;
delay(600);
lcd.clear();
lcd.setCursor(0,0);
lcd.print("MAP[mmHG]");


Serial.write(0x06);  //request

while(Serial.available() < 2); //wait until there are two bytes in the buffer


MAP = Serial.read() << 8 ;   //read MSB into MAP
MAP += Serial.read();        //read LSB into MAP
MAP1 = (MAP * 2.8759 + 91); //operation

lcd.setCursor(0,1);
lcd.print(MAP1); //display


}

This code is blocking so you may want to change from a while loop to a delay and some if statements. Also I'm not sure if your LCD prints MSB or LSB first, I assumed MSB.

Upvotes: 2

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