dataType

boolean (8 bit) - simple logical true/false
byte (8 bit) - unsigned number from 0-255
char (8 bit) - signed number from -128 to 127.
unsigned char (8 bit) - same as ‘byte’
word (16 bit) - unsigned number from 0-65535
unsigned int (16 bit)- the same as ‘word’.
int (16 bit) - signed number from -32768 to 32767.
unsigned long (32 bit) - unsigned number from 0-4,294,967,295.
long (32 bit) - signed number from -2,147,483,648 to 2,147,483,647
float (32 bit) - signed number from -3.4028235E38 to 3.4028235E38.

資料型態	說明	記憶體長度	數值範圍
boolean	布林	8 bits	true (1, HIGH), false (0, LOW)
byte	位元組	8 bits	0~255
char	字元	8 bits	-128~127
short	短整數	16 bits	-32768~32767
int	整數	16 bits	-32768~32767
word	字	16 bits	0~65535
long	長整數	32 bits	-2147483648~2147483647
float	浮點數	32 bits	+-3.4028235e+38
double	倍精度浮點數	32 bits	>+-3.4028235e+38

C,C++ 跨平台: (現代 C 語言的寫法)

帶正負號的整數使用 int8_t、int16_t、int32_t、int64_t
不帶號的整數使用 uint8_t、uint16_t、uint32_t、uint64_t
32 與 64 位元長的浮點數使用 float 與 double

void setup() {
Serial.begin(9600);
}

void loop() {
Serial.println("--- Variable type: Size in SRAM (bytes) ---");

/*
C standard data type "unsigned int length 8 bits".
Occupies one byte of memory.
http://arduino.cc/forum/index.php/topic,41590.0.html
http://en.wikipedia.org/wiki/Stdint.h#Fixed_width_integer_types
*/
Serial.print("uint8_t: ");
Serial.println(sizeof(uint8_t));

/*
A boolean holds one of two values, true or false.
Each boolean variable occupies one byte of memory.
http://arduino.cc/en/Reference/BooleanVariables
*/
Serial.print("boolean: ");
Serial.println(sizeof(boolean));
/*
A data type that takes up 1 byte of memory that stores a character value.
Character literals are written in single quotes, like this: 'A' (for multiple
characters - strings - use double quotes: "ABC").
http://arduino.cc/en/Reference/Char
*/
Serial.print("char: ");
Serial.println(sizeof(char));

/*
An unsigned data type that occupies 1 byte of memory. Same as the byte datatype.
The unsigned char datatype encodes numbers from 0 to 255.
For consistency of Arduino programming style, the byte data type is to be preferred.
http://arduino.cc/en/Reference/UnsignedChar
*/
Serial.print("unsigned char: ");
Serial.println(sizeof(unsigned char));

/*
A byte stores an 8-bit unsigned number, from 0 to 255.
http://arduino.cc/en/Reference/Byte
*/
Serial.print("byte: ");
Serial.println(sizeof(byte));

/*
Integers are your primary datatype for number storage, and store a 2 byte value.
This yields a range of -32,768 to 32,767 (minimum value of -2^15 and a maximum value of (2^15) - 1).
http://arduino.cc/en/Reference/Int
*/
Serial.print("int: ");
Serial.println(sizeof(int));

/*
Unsigned ints (unsigned integers) are the same as ints in that they store a 2 byte value.
Instead of storing negative numbers however they only store positive values, yielding a
useful range of 0 to 65,535 (2^16) - 1).
http://arduino.cc/en/Reference/UnsignedInt
*/
Serial.print("unsigned int: ");
Serial.println(sizeof(unsigned int));

// A word stores a 16-bit unsigned number, from 0 to 65535.
// Same as an unsigned int.
// http://arduino.cc/en/Reference/Word
Serial.print("word: ");
Serial.println(sizeof(word));

/*
Long variables are extended size variables for number storage, and store 32 bits (4 bytes),
from -2,147,483,648 to 2,147,483,647.
http://arduino.cc/en/Reference/Long
*/
Serial.print("long: ");
Serial.println(sizeof(long));

/*
Unsigned long variables are extended size variables for number storage, and store 32 bits (4 bytes).
Unlike standard longs unsigned longs won't store negative numbers, making their range from 0
to 4,294,967,295 (2^32 - 1).
http://arduino.cc/en/Reference/UnsignedLong
*/
Serial.print("unsigned long: ");
Serial.println(sizeof(unsigned long));

/*
Datatype for floating-point numbers, a number that has a decimal point.
Floating-point numbers can be as large as 3.4028235E+38 and as low as -3.4028235E+38.
They are stored as 32 bits (4 bytes) of information.
http://arduino.cc/en/Reference/Float
*/
Serial.print("float: ");
Serial.println(sizeof(float));

/*
Double precision floating point number. Occupies 4 bytes.
The double implementation on the Arduino is currently exactly the same as the float,
with no gain in precision.
http://arduino.cc/en/Reference/Double
*/
Serial.print("double: ");
Serial.println(sizeof(double));

delay(8500);
}

unsigned int a=(data>>4) & 0xF; //top 4 bits of data
unsigned int b=data & 0xF;// bottom 4 bits of data

Why “& 0xF” in the first line? Because if your data is more than 8 bits,
you want to remove the higher ones from the result (called masking),
leaving only the single nybble of 4 bits.

send the 16-bit value as two 8-bit values
Serial.write(0xCC);//send the start byte
Serial.write(sensorVal>>8 &0xff);//send the higher byte
Serial.write(sensorVal & 0xff);// send the lower byte

uint16_t data = 1000;
uint8_t buf[2];
buf[0] = data & 255;
buf[1] = (data >> 8) & 255;
Serial.write(buf, 2);

使用union

#define Led 12
union uData
{
byte b[2];
int value;
};
union uData data;
#define Led 8
void setup() {
pinMode(Led,OUTPUT);
digitalWrite(Led,0);
data.b[0]=0x34;
data.b[1]=0x12;
if(data.value==0x1234)
digitalWrite(Led,1);
}

void loop() {
}

2個Arduino
使用Serial.write() 與Serial.read()傳送2 Byte data

傳送端

union uData
{
byte b[2];
int value;
};

union uData data;
void setup() {
Serial.begin(9600);
delay(1000);
}

void loop() {
data.value=0x3456;
//while(!(UCSR0A & (1<<UDRE0)));// 若UDRE0=0 等待
Serial.write(0x21);//起始字元
//while(!(UCSR0A & (1<<UDRE0)));// 若UDRE0=0 等待
Serial.write(data.b[0]);
// while(!(UCSR0A & (1<<UDRE0)));// 若UDRE0=0 等待
Serial.write(data.b[1]);
delay(1000);
}

或

union uData
{
byte b[2];
int value;
};

union uData data;
void setup() {
Serial.begin(9600);
delay(1000);
}

void loop() {
data.value=0x3456;
Serial.write(0x21);//起始字元
Serial.write(data.b,2);
delay(1000);
}

接收端

#define Led 12
union uData
{
byte b[2];
int value;
};

union uData data;

void setup() {
Serial.begin(9600);
pinMode(Led,OUTPUT);
digitalWrite(Led,1);
}

void loop() {
if(Serial.available()>0)
{
if(Serial.read()==0x21) //判斷是否為起始字元
{
   //delay(10);//若資料傳遞不正確可再加長
   // Wait until data is received (不用delay)
   while ( !(UCSR0A & (1 << RXC0)) ) ;
   data.b[0]=Serial.read();

//delay(10);//若資料傳遞不正確可再加長
// Wait until data is received (不用delay)
   while ( !(UCSR0A & (1 << RXC0)) ) ;
   data.b[1]=Serial.read();
   if(data.value==0x3456)
    { //Toggle D12
        digitalWrite(Led,1-digitalRead(Led));
      //asm("SBI 0x03,4");
    }
}

}
}

或

Arduino序列埠通訊程式Serial.read()讀取到 ÿ 字元(web)

Arduino 傳兩筆資料到 Android (app inventor)手機(web)