[英]Serial read write with Baud rate 9600 , parity none, data bits 8 and stop bits 2. Unable to communicate with device
I am working on project which requires to send command in hex with device setting as follows : Baud rate : 9600, Parity : None, Stop bits : 2 , data bits : 8 (9600, 8N2). 我正在进行一个项目,该项目需要使用以下设备设置以十六进制形式发送命令:波特率:9600,奇偶校验:无,停止位:2,数据位:8(9600,8N2)。
I have verified by sending data to device with minicom. 我已通过将数据发送到带有minicom的设备进行了验证。 I am able to see data on CRO.
我可以查看CRO上的数据。 But when I am sending data via C code and unable to see data on CRO and getting program output as FFFFF always for read function.
但是,当我通过C代码发送数据并且无法在CRO上看到数据并且无法始终以读取功能将程序输出为FFFFF时。
Source code for serial read and write : 串行读写的源代码:
int32_t Read()
{
printf("Entering Read function \n");
int fd;
fd = open("/dev/ttyS1", O_RDWR | O_NOCTTY | O_NDELAY);
int j=0;
if (fd == -1)
{
perror("open_port: Unable to open /dev/ttyS1\n");
exit(1);
}
else
{
printf("Port /dev/ttyS1 opened successfully\n");
}
//---------- Setting the Attributes of the serial port using termios structure ---------
struct termios SerialPortSettings; // Create the structure
tcgetattr(fd, &SerialPortSettings); // Get the current attributes of the Serial port
cfsetispeed(&SerialPortSettings,B9600); // Set Read Speed as 9600
cfsetospeed(&SerialPortSettings,B9600); // Set Write Speed as 9600
SerialPortSettings.c_cflag &= ~PARENB; // Disables the Parity Enable bit(PARENB),So No Parity
SerialPortSettings.c_cflag &= ~PARODD; // added
SerialPortSettings.c_cflag |= CS8; // Set the data bits = 8
SerialPortSettings.c_cflag &= CSTOPB; // CSTOPB = 2 Stop bits
SerialPortSettings.c_cflag &= ~CSIZE; // Clears the mask for setting the data size
SerialPortSettings.c_cflag &= ~CRTSCTS; // No Hardware flow Control
SerialPortSettings.c_cflag |= (CREAD | CLOCAL); // Enable receiver,Ignore Modem Control lines
SerialPortSettings.c_lflag =0; /* RAW input */ // added
SerialPortSettings.c_iflag &= ~(IXON | IXOFF | IXANY); // Disable XON/XOFF flow control both i/p and o/p
SerialPortSettings.c_iflag &= ~(ICANON | ECHO | ECHOE | ISIG); // Non Cannonical mode
SerialPortSettings.c_cc[VMIN] = 0; // added for testing // added 1 sec
SerialPortSettings.c_cc[VTIME] = 5; // added for testing // added
SerialPortSettings.c_iflag = 0; /* SW flow control off, no parity checks etc */ // added
SerialPortSettings.c_oflag &= ~OPOST;// No Output Processing
if((tcsetattr(fd,TCSANOW,&SerialPortSettings)) != 0) // Set the attributes to the termios structure
printf("\n ERROR ! in Setting attributes");
else
printf("\n BaudRate = 9600 \n StopBits = 2 \n Parity = None\n");
//------------------------------- Write data to serial port -----------------------------
unsigned char write_buffer[] = {0x28,0x11,0xDF,0xBC}; // Buffer containing characters to write into port
int bytes_written = 0; // Value for storing the number of bytes written to the port
for(j=0;j<4;j++)
{
bytes_written = write(fd,write_buffer[j],sizeof(write_buffer));// use write() to send data to port
// "fd" - file descriptor pointing to the opened serial port
// "write_buffer" - address of the buffer containing data
// "sizeof(write_buffer)" - No of bytes to write
//
printf("Byte written : %x\n",write_buffer[j]);
printf("\n %d Bytes written to ttyS1", bytes_written);
printf("\n +----------------------------------+\n\n");
}
sleep(2);
//------------------------------- Read data from serial port -----------------------------
tcflush(fd, TCIFLUSH); // Discards old data in the rx buffer
unsigned char read_buffer[40]; // Buffer to store the data received
int bytes_read = 0; // Number of bytes read by the read() system call
int i = 0;
bytes_read = read(fd,&read_buffer,40); // Read the data
printf("\n\n Bytes Rxed -%x", bytes_read); // Print the number of bytes read
printf("\n\n ");
for(i=0;i<bytes_read;i++) //printing only the received characters
printf("%x",(int)(*(unsigned char*)(&read_buffer[i])));
printf("\n +----------------------------------+\n\n\n");
close(fd); // Close the serial port
printf("Exiting Read function \n");
}
Output : 输出:
Entering Read function
Port /dev/ttyS1 opened successfully
BaudRate = 9600
StopBits = 2
Parity = None
Byte written : 28
-1 Bytes written to ttyS1
+----------------------------------+
Byte written : 11
-1 Bytes written to ttyS1
+----------------------------------+
Byte written : df
-1 Bytes written to ttyS1
+----------------------------------+
Byte written : bc
-1 Bytes written to ttyS1
+----------------------------------+
Bytes Rxed -ffffffff
+----------------------------------+
Exiting Read function
1st of all add error checking to this call: 首先,向该调用添加错误检查:
tcgetattr(fd, &SerialPortSettings);
like 喜欢
if (0 > tcgetattr(fd, &SerialPortSettings))
{
/* log and handle error */
}
Then here 那这边
SerialPortSettings.c_cflag |= CS8;
you set the data bits. 您设置数据位。
Two lines below you clear it 您下方的两行将其清除
SerialPortSettings.c_cflag &= ~CSIZE;
Do this the other way round. 反之亦然。
Also this 还有这个
SerialPortSettings.c_cflag &= CSTOPB;
unsets. 未设置。
If you want to use 2 stop bits set it by doing 如果要使用2个停止位,请通过以下方式进行设置
SerialPortSettings.c_cflag |= CSTOPB;
Instead of just doing 不仅仅是做
SerialPortSettings.c_oflag &= ~OPOST;
do 做
SerialPortSettings.c_oflag = 0;
The code calls write()
wrongly. 该代码错误地调用了
write()
。 This 这个
for(j=0;j<4;j++)
{
bytes_written = write(fd,write_buffer[j],sizeof(write_buffer));
ought to be 必定是
for(j=0;j<4;j++)
{
bytes_written = write(fd, &write_buffer[j], 1)
Or just drop the loop and do 或者只是放弃循环并做
bytes_written = write(fd, write_buffer, sizeof write_buffer);
The call to read()
is wrong as well. 调用
read()
也是错误的。
It should be 它应该是
bytes_read = read(fd, read_buffer, ...
For some of those mistakes with write
and read
the compiler should have warned you about. 对于一些与错误的
write
和read
编译器应该警告你一下。
Please also note that read()
and write()
return ssize_t
not int
. 另请注意,
read()
和write()
返回ssize_t
而不是int
。
Last not least I doubt flushing the input buffer ( tcflush(fd, TCIFLUSH);
) before reading it makes sense. 最后,我特别怀疑在读取有意义的输入之前先清空输入缓冲区(
tcflush(fd, TCIFLUSH);
)。
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