UART

The UART devices are registered on VFS as device files accessible via startard IO system calls and termios API.

UART devices are registed under /dev/ttySx, where x is uart number starting from 0.

On both MT6261/MT2503 based GSM modules and RDA8910 based 4G LTE modules, three hardware uart interfaces are available. On RDA8955 based modules two hardware UARTs are available.

On devices with on-board GNSS (SIM868/N58-CA/EC200U), 2 UARTs are exposed on external pins whereas 1 UART is connected to GNSS as a dedicated interface.

On modules like MC60/MC20, GNSS port is also exposed on outside pins which provides freedom to select any UART port to be connected to GNSS module.

So if module has three physical UART interface, the three UART device files will be:

• /dev/ttyS0

• /dev/ttyS1

• /dev/ttyS2

Each device file supports standard system calls for IO operations (open, read, write, close etc.)

Serial port parameters can be accessed by standard termios API (similar to linux).

Example Usage

#include <unistd.h>
#include <fcntl.h>
#include <termios.h>

/* Open uart */
int fd = open("/dev/ttyS0");

/* Set baudrate */
tcgetattr(fd, &t);
cfsetspeed(&t, B9600);
tcsetattr(fd, TCSANOW, &t);

/* write on uart */
write(fd, "Test", 4);

/* read */
int ret;
char buf[10];

ret = read(fd, buf, sizeof(buf));

Application Example

waybyte/example-uart

4G LTE Module Pin Mapping

UART Function	EC600U	EC200U	N58	N716	L610	EG915U
UART0 TXD	Pin 32	Pin 67	Pin 46	Pin 59	Pin 67	Pin 35
UART0 RXD	Pin 31	Pin 68	Pin 47	Pin 58	Pin 68	Pin 34
UART1 TXD	Pin 124	Pin 139	Pin 69	Pin 11	Pin 139	Pin 27
UART1 RXD	Pin 123	Pin 136	Pin 70	Pin 12	Pin 136	Pin 28
UART2 TXD	Pin 103	Pin 82	GNSS RX	Pin 9	Pin 82	Pin 23
UART2 RXD	Pin 104	Pin 81	GNSS TX	Pin 10	Pin 81	Pin 22

GSM Module Pin Mapping

RDA8955 based modules

UART Function	M590	MC65	A9
UART0 TXD	Pin 8	Pin 34	Pin 54
UART0 RXD	Pin 7	Pin 33	Pin 53
UART1 TXD	Pin 58	Pin 25	Pin 50
UART1 RXD	Pin 59	Pin 24	Pin 49

MT2503/MT6261/MT2625 based modules

UART Function	MC20 Pin MC20U Pin	M56 Pin	MC60 Pin	M66 Pin	SIM868 Pin
UART0 TXD	Pin 34	Pin 25	Pin 33	Pin 17	Pin 1
UART0 RXD	Pin 33	Pin 36	Pin 34	Pin 18	Pin 2
UART1 TXD	Pin 25	Pin 41	Pin 25	Pin 29	Pin 22
UART1 RXD	Pin 24	Pin 40	Pin 24	Pin 28	Pin 23
UART2 TXD	Pin 29	Pin 13	Pin 29	Pin 39	–
UART2 RXD	Pin 30	Pin 2	Pin 30	Pin 38	–

API Reference

Termios Systemcall Support