SoftwareSerial Library

The SoftwareSerial library allows serial communication on other digital pins of an Arduino board.

AUTHOR:

Arduino

LAST REVISION:

04/26/2023, 09:28 AM

The SoftwareSerial library allows serial communication on other digital pins of an Arduino board, using software to replicate the functionality (hence the name “SoftwareSerial”). It is possible to have multiple software serial ports with speeds up to 115200 bps. A parameter enables inverted signaling for devices which require that protocol.

The version of SoftwareSerial included in 1.0 and later is based on the NewSoftSerial library by ‘Mikal Hart’.

To use this library:

1
#include <SoftwareSerial.h>

Limitations of This Library

SoftwareSerial library has the following known limitations:

• It cannot transmit and receive data at the same time.
• If using multiple software serial ports, only one can receive data at a time.
• Not all pins on the Mega and Mega 2560 boards support change interrupts, so only the following can be used for RX: 10, 11, 12, 13, 14, 15, 50, 51, 52, 53, A8 (62), A9 (63), A10 (64), A11 (65), A12 (66), A13 (67), A14 (68), A15 (69).
  Not all pins on the Leonardo and Micro boards support change interrupts, so only the following can be used for RX: 8, 9, 10, 11, 14 (MISO), 15 (SCK), 16 (MOSI).
• On Arduino or Genuino 101 boards the current maximum RX speed is 57600bps.
• On Arduino or Genuino 101 boards RX doesn’t work on digital pin 13.

If your project requires simultaneous data flows, see Paul Stoffregen’s AltSoftSerial library.

Examples

• SoftwareSerial example: sometimes one serial port just isn’t enough!
• Two port receive: Work with multiple software serial ports.

Methods

SoftwareSerial
(
)

Create an instance of a SoftwareSerial object. Multiple SoftwareSerial objects may be created, however only one can be active at a given moment.

Syntax

1
SoftwareSerial(rxPin, txPin, inverse_logic)

Parameters

• rxPin: the pin on which to receive serial data.
• txPin: the pin on which to transmit serial data.
• inverse_logic: used to invert the sense of incoming bits (the default is normal logic). If set, SoftwareSerial treats a LOW (0v on the pin, normally) on the RX pin as a 1-bit (the idle state) and a HIGH (5V on the pin, normally) as a 0-bit. It also affects the way that it writes to the TX pin. Default value is false.

Returns

None.

Example

1
#
include
 
<SoftwareSerial.h>
2

3
const 
byte
 rxPin 
=
 
2
;
4
const 
byte
 txPin 
=
 
3
;
5

6
7
SoftwareSerial
 
mySerial
 
(
rxPin
,
 txPin
)
;

See also

available
(
)

Get the number of bytes (characters) available for reading from a software serial port. This is data that has already arrived and stored in the serial receive buffer.

Syntax

1
mySerial.available()

Parameters

None.

Returns

The number of bytes available to read.

Example

1
#
include
 
<SoftwareSerial.h>
2

3
#
define
 
rxPin
 
10
4
#
define
 
txPin
 
11
5

6
7
SoftwareSerial
 mySerial 
=
  
SoftwareSerial
(
rxPin
,
 txPin
)
;
8

9
void
 
setup
(
)
  
{
10
    
11
    
pinMode
(
rxPin
,
 
INPUT
)
;
12
    
pinMode
(
txPin
,
 
OUTPUT
)
;
13
    
14
    
15
    mySerial
.
begin
(
9600
)
;
16
}
17

18
void
 
loop
(
)
 
{
19
    
if
 
(
mySerial
.
available
(
)
 
>
 
0
)
 
{
20
        mySerial
.
read
(
)
;
21
    
}
22
}

See also

begin
(
)

Sets the speed (baud rate) for the serial communication. Supported baud rates are: 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 28800, 31250, 38400, 57600, and 115200 bauds.

Syntax

1
mySerial.begin(speed)

Parameters

• speed: the desired baud rate (long). Supported baud rates are: 300, 600, 1200, 2400, 4800, 9600, 14400, 19200, 28800, 31250, 38400, 57600, and 115200 bauds.

Returns

None.

Example

1
#
include
 
<SoftwareSerial.h>
2

3
#
define
 
rxPin
 
10
4
#
define
 
txPin
 
11
5

6
7
SoftwareSerial
 mySerial 
=
  
SoftwareSerial
(
rxPin
,
 txPin
)
;
8

9
void
 
setup
(
)
  
{
10
    
11
    
pinMode
(
rxPin
,
 
INPUT
)
;
12
    
pinMode
(
txPin
,
 
OUTPUT
)
;
13

14
    
15
    mySerial
.
begin
(
9600
)
;
16
}
17

18
void
 
loop
(
)
 
{
19
    
20
}

See also

isListening
(
)

Tests to see if requested software serial object is actively listening.

Syntax

1
mySerial.isListening()

Parameters

None.

Returns

Boolean.

Example

1
#
include
 
<SoftwareSerial.h>
2

3
4
SoftwareSerial
 
portOne
(
10
,
 
11
)
;
5

6
void
 
setup
(
)
 
{
7
    
8
    
Serial
.
begin
(
9600
)
;
9

10
    
11
    portOne
.
begin
(
9600
)
;
12
}
13

14
void
 
loop
(
)
 
{
15
    
if
 
(
portOne
.
isListening
(
)
)
 
{
 
16
        
Serial
.
println
(
"portOne is listening!"
)
;
17
    
}
18

19
    

See also

overflow
(
)

Tests to see if a SoftwareSerial buffer overflow has occurred. Calling this function clears the overflow flag, meaning that subsequent calls will return false unless another byte of data has been received and discarded in the meantime. The SoftwareSerial buffer can hold up to 64 bytes.

Syntax

1
mySerial.overflow()

Parameters

None.

Returns

Boolean.

Example

1
#
include
 
<SoftwareSerial.h>
2

3
4
SoftwareSerial
 
portOne
(
10
,
 
11
)
;
5

6
void
 
setup
(
)
 
{
7
    
8
    
Serial
.
begin
(
9600
)
;
9

10
    
11
    portOne
.
begin
(
9600
)
;
12
}
13

14
void
 
loop
(
)
 
{
15
    
if
 
(
portOne
.
overflow
(
)
)
 
{
16
        
Serial
.
println
(
"portOne overflow!"
)
;
17
    
}
18

19
    

See also

peek
(
)

Return a character that was received on the RX pin of the software serial port. Unlike read(), however, subsequent calls to this function will return the same character. Note that only one SoftwareSerial object can receive incoming data at a time (select which one with the listen() function).

Syntax

1
mySerial.peek()

Parameters

None.

Returns

The character read or -1 if none is available.

Example

1
#
include
 
<SoftwareSerial.h>
2

3
4
SoftwareSerial
 
mySerial
(
10
,
 
11
)
;
5

6
void
 
setup
(
)
 
{
7
    
8
    mySerial
.
begin
(
9600
)
;
9
}
10

11
void
 
loop
(
)
 
{
12
    char c 
=
 mySerial
.
peek
(
)
;
13
}

See also

read
(
)

Return a character that was received on the RX pin of the SoftwareSerial objecto. Note that only one SoftwareSerial object can receive incoming data at a time (select which one with the listen() function).

Syntax

1
mySerial.read()

Parameters

None.

Returns

The character read or -1 if none is available.

Example

1
#
include
 
<SoftwareSerial.h>
2

3
4
SoftwareSerial
 
mySerial
(
10
,
 
11
)
;
5

6
void
 
setup
(
)
 
{
7
    
8
    mySerial
.
begin
(
9600
)
;
9
}
10

11
void
 
loop
(
)
 
{
12
    char c 
=
 mySerial
.
read
(
)
;
13
}

See also

Prints data to the transmit pin of the SoftwareSerial object. Works the same as the Serial.print() function.

Syntax

1
mySerial.print(val)

Parameters

• val: the value to print.

Returns

The number of bytes written (reading this number is optional).

Example

1
#
include
 
<SoftwareSerial.h>
2

3
4
SoftwareSerial
 
mySerial
(
10
,
 
11
)
;
5

6
int
 analogValue
;
7

8
void
 
setup
(
)
 
{
9
    
10
    mySerial
.
begin
(
9600
)
;
11
}
12

13
void
 
loop
(
)
 
{
14
    
15
    analogValue 
=
 
analogRead
(
A0
)
;
16

17
    
18
    mySerial
.
print
(
analogValue
)
;
         
19
    mySerial
.
print
(
"\t"
)
;
                
20
    mySerial
.
print
(
analogValue
,
 DEC
)
;
    
21
    mySerial
.
print
(
"\t"
)
;
                
22
    mySerial
.
print
(
analogValue
,
 HEX
)
;
    
23
    mySerial
.
print
(
"\t"
)
;
                
24
    mySerial
.
print
(
analogValue
,
 OCT
)
;
    
25
    mySerial
.
print
(
"\t"
)
;
                
26
    mySerial
.
print
(
analogValue
,
 BIN
)
;
    
27
    mySerial
.
print
(
"\t"
)
;
                
28
    mySerial
.
print
(
analogValue
/
4
,
 BYTE
)
;
 
29
                                         
30
                                         
31

32
    mySerial
.
print
(
"\t"
)
;
                
33
    mySerial
.
println
(
)
;
                  
34

35
    
36
    
delay
(
10
)
;
37
}

See also

println
(
)

Prints data to the transmit pin of the SoftwareSerial object followed by a carriage return and line feed. Works the same as the Serial.println() function.

Syntax

1
mySerial.println(val)

Parameters

• val: the value to print.

Returns

The number of bytes written (reading this number is optional).

Example

1
#
include
 
<SoftwareSerial.h>
2

3
4
SoftwareSerial
 
mySerial
(
10
,
 
11
)
;
5

6
int
 analogValue
;
7

8
void
 
setup
(
)
 
{
9
    
10
    mySerial
.
begin
(
9600
)
;
11
}
12

13
void
 
loop
(
)
 
{
14
    
15
    analogValue 
=
 
analogRead
(
A0
)
;
16

17
    
18
    mySerial
.
print
(
analogValue
)
;
         
19
    mySerial
.
print
(
"\t"
)
;
                
20
    mySerial
.
print
(
analogValue
,
 DEC
)
;
    
21
    mySerial
.
print
(
"\t"
)
;
                
22
    mySerial
.
print
(
analogValue
,
 HEX
)
;
    
23
    mySerial
.
print
(
"\t"
)
;
                
24
    mySerial
.
print
(
analogValue
,
 OCT
)
;
    
25
    mySerial
.
print
(
"\t"
)
;
                
26
    mySerial
.
print
(
analogValue
,
 BIN
)
;
    
27
    mySerial
.
print
(
"\t"
)
;
                
28
    mySerial
.
print
(
analogValue
/
4
,
 BYTE
)
;
 
29
                                         
30
                                         
31

32
    mySerial
.
print
(
"\t"
)
;
                
33
    mySerial
.
println
(
)
;
                  
34

35
    
36
    
delay
(
10
)
;
37
}

See also

listen
(
)

Enables the selected SoftwareSerial object to listen. Only one SoftwareSerial object can listen at a time; data that arrives for other ports will be discarded. Any data already received is discarded during the call to listen() function (unless the given instance is already listening).

Syntax

1
mySerial.listen()

Parameters

None.

Returns

Returns true if it replaces another.

Example

1
#
include
 
<SoftwareSerial.h>
2

3
4
SoftwareSerial
 
portOne
(
10
,
 
11
)
;
5

6
7
SoftwareSerial
 
portTwo
(
8
,
 
9
)
;
8

9
void
 
setup
(
)
 
{
10
    
11
    
Serial
.
begin
(
9600
)
;
12

13
    
14
    portOne
.
begin
(
9600
)
;
15
    portTwo
.
begin
(
9600
)
;
16
}
17

18
void
 
loop
(
)
 
{
19
    
20
    portOne
.
listen
(
)
;
21
    
22
    
if
 
(
portOne
.
isListening
(
)
)
 
{
23
        
Serial
.
println
(
"portOne is listening!"
)
;
24
    
}
 
else
 
{
25
        
Serial
.
println
(
"portOne is not listening!"
)
;
26
    
}
27

28
    
if
 
(
portTwo
.
isListening
(
)
)
 
{
29
        
Serial
.
println
(
"portTwo is listening!"
)
;
30
    
}
 
else
 
{
31
        
Serial
.
println
(
"portTwo is not listening!"
)
;
32
    
}
33
}

See also

write
(
)

Prints data to the transmit pin of the SoftwareSerial object as raw bytes. Works the same as the Serial.write()function.

Syntax

1
mySerial.write(val)

Parameters

• val: the binary value to print.

Returns

The number of bytes written (reading this number is optional).

Example

1
#
include
 
<SoftwareSerial.h>
2

3
4
SoftwareSerial
 
mySerial
(
10
,
 
11
)
;
5

6
void
 
setup
(
)
 
{
7
    
8
    mySerial
.
begin
(
9600
)
;
9
}
10

11
void
 
loop
(
)
 
{
12
    
13
    mySerial
.
write
(
45
)
;
14

15
    
16
    
int
 bytesSent 
=
 mySerial
.
write
(
“hello”
)
;
17
}

See also