CC = gcc

CFLAGS = -Wall -Wextra -Wshadow -Wformat-nonliteral -Wformat-security -Wtype-limits -O2

objects = rs232.o

all: test_rx test_tx

test_rx : $(objects) demo_rx.o

$(CC) $(objects) demo_rx.o -o test_rx

test_tx : $(objects) demo_tx.o

$(CC) $(objects) demo_tx.o -o test_tx

demo_rx.o : demo_rx.c rs232.h

$(CC) $(CFLAGS) -c demo_rx.c -o demo_rx.o

demo_tx.o : demo_tx.c rs232.h

$(CC) $(CFLAGS) -c demo_tx.c -o demo_tx.o

rs232.o : rs232.h rs232.c

$(CC) $(CFLAGS) -c rs232.c -o rs232.o

clean :

$(RM) test_rx test_tx $(objects) demo_rx.o demo_tx.o rs232.o

RS-232 for Linux, FreeBSD and windows

Website: https://www.teuniz.net/RS-232/

No merge requests. If you want to report a bug, create an issue.

Library: RS-232

Author: Teunis van Beelen

Url: http://www.teuniz.net/RS-232/

E-mail: teuniz@protonmail.com

License: GPLv3

Last revision: August, 2020

int RS232_OpenComport(int comport_number, int baudrate, const char * mode, int flowctrl)

Opens the comport, comportnumber starts with 0 (see the list of numbers).

Baudrate is expressed in baud per second i.e 115200 (see the list of possible baudrates).

Mode is a string in the form of "8N1", "7E2", etc.

8N1 means eight databits, no parity, one stopbit. If in doubt, use 8N1 (see the list of possible modes).

If flowctrl is set to 0, no flow control is used.

If flowctrl is set to 1, hardware flow control is enabled using the RTS/CTS lines.

Returns 1 in case of an error.

In case the comport is already opened (by another process),

it will not open the port but raise an error instead.

int RS232_PollComport(int comport_number, unsigned char *buf, int size)

Gets characters from the serial port (if any). Buf is a pointer to a buffer

and size the size of the buffer in bytes.

Returns the amount of received characters into the buffer. This can be less than size or zero!

It does not block or wait, it returns immediately, no matter if any characters have been received or not.

After succesfully opening the COM-port, connect this function to a timer.

The timer should have an interval of approx. 20 to 100 milliSeconds.

Do not forget to stop the timer before closing the COM-port.

Allways check the return value! The return value tells you how many bytes

are actually received and present in your buffer!

int RS232_SendByte(int comport_number, unsigned char byte)

Sends a byte via the serial port. Returns 1 in case of an error.

int RS232_SendBuf(int comport_number, unsigned char *buf, int size)

Sends multiple bytes via the serial port. Buf is a pointer to a buffer

and size the size of the buffer in bytes.

Returns -1 in case of an error, otherwise it returns the amount of bytes sent.

This function blocks (it returns after all the bytes have been processed).

void RS232_CloseComport(int comport_number)

Closes the serial port.

void RS232_cputs(int comport_number, const char *text)

Sends a string via the serial port. String must be null-terminated.

int RS232_GetPortnr(const char *devname)

Returns the comport number based on the device name e.g. "ttyS0" or "COM1".

(Doesn't mean the device actually exists!)

Returns -1 when not found.

The following functions are normally not needed but can be used to set or check the status of the control-lines:

================================================================================================================

void RS232_enableDTR(int comport_number)

Sets the DTR line high (active state).

void RS232_disableDTR(int comport_number)

Sets the DTR line low (non active state).

void RS232_enableRTS(int comport_number)

Sets the RTS line high (active state). Do not use this function if hardware flow control is enabled!

void RS232_disableRTS(int comport_number) Do not use this function if hardware flow control is enabled!

Sets the RTS line low (non active state).

int RS232_IsRINGEnabled(int comport_number)

Checks the status of the RING-pin. Returns 1 when the the RING line is high (active state), otherwise 0.

int RS232_IsDSREnabled(int comport_number)

Checks the status of the DSR-pin. Returns 1 when the the DSR line is high (active state), otherwise 0.

int RS232_IsCTSEnabled(int comport_number)

Checks the status of the CTS-pin. Returns 1 when the the CTS line is high (active state), otherwise 0.

int RS232_IsDCDEnabled(int comport_number)

Checks the status of the DCD-pin. Returns 1 when the the DCD line is high (active state), otherwise 0.

The following functions are normally not needed but can be used to empty the rx/tx buffers:

===========================================================================================

("discards data written to the serial port but not transmitted, or data received but not read")

void RS232_flushRX(int comport_number)

Flushes data received but not read.

void RS232_flushTX(int comport_number)

Flushes data written but not transmitted.

void RS232_flushRXTX(int comport_number)

Flushes both data received but not read, and data written but not transmitted.

Notes:

You don't need to call RS232_PollComport() when you only want to send characters.

Sending and receiving do not influence eachother.

The os (kernel) has an internal buffer of 4096 bytes (for traditional onboard serial ports).

USB/Serial-converter drivers use much bigger buffers (multiples of 4096).

If this buffer is full and a new character arrives on the serial port,

the oldest character in the buffer will be overwritten and thus will be lost.

After a successfull call to RS232_OpenComport(), the os will start to buffer incoming characters.

tip: To get access to the serial port on Linux, you need to be a member of the group "dialout".

Note: Traditional (on-board) UART's usually have a speed limit of max. 115200 baud.

Special cards and USB to Serial converters can usually be set to higher baudrates.

List of comport numbers, possible baudrates and modes:

Linux windows

0 ttyS0 COM1

1 ttyS1 COM2

2 ttyS2 COM3

3 ttyS3 COM4

4 ttyS4 COM5

5 ttyS5 COM6

6 ttyS6 COM7

7 ttyS7 COM8

8 ttyS8 COM9

9 ttyS9 COM10

10 ttyS10 COM11

11 ttyS11 COM12

12 ttyS12 COM13

13 ttyS13 COM14

14 ttyS14 COM15

15 ttyS15 COM16

16 ttyUSB0 COM17

17 ttyUSB1 COM18

18 ttyUSB2 COM19

19 ttyUSB3 COM20

20 ttyUSB4 COM21

21 ttyUSB5 COM22

22 ttyAMA0 COM23

23 ttyAMA1 COM24

24 ttyACM0 COM25

25 ttyACM1 COM26

26 rfcomm0 COM27

27 rfcomm1 COM28

28 ircomm0 COM29

29 ircomm1 COM30

30 cuau0 COM31

31 cuau1 COM32

32 cuau2 n.a.

33 cuau3 n.a.

34 cuaU0 n.a.

35 cuaU1 n.a.

36 cuaU2 n.a.

37 cuaU3 n.a.

Linux windows

50 n.a.

75 n.a.

110 110

134 n.a.

150 n.a.

200 n.a.

300 300

600 600

1200 1200

1800 n.a.

2400 2400

4800 4800

9600 9600

19200 19200

38400 38400

57600 57600

115200 115200

230400 128000

460800 256000

500000 500000

576000 n.a.

921600 921600

1000000 1000000

1152000 n.a.

1500000 1500000

2000000 2000000

2500000 n.a.

3000000 3000000

3500000 n.a.

4000000 n.a.

Mode

8N1

8O1

8E1

8N2

8O2

8E2

7N1

7O1

7E1

7N2

7O2

7E2

6N1

6O1

6E1

6N2

6O2

6E2

5N1

5O1

5E1

5N2

5O2

5E2