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背景:
与硬件打资产的程序最简单者应属串口的通信，下面是来自于ibm的串口程序教程及代码。也许是一个好的开始。
正文:
1. 串口常识
串行口的典型代表是RS－232－C 及其兼容插口，25 针串行口还具有20mA 电流环接
口功能，用9,11,18,25针来实现。
RS-232-C 是美国电子工业协会EIA（Electronic Industry Association）制定的一种串行物理接口标准。RS 是英文“推荐标准”的缩写，232 为标识号，C 表示修改次数。RS-232-C 总线标准设有25 条信号线，包括一个主通道和一个辅助通道，在多数情况下主要使用主通道，对于一般双工通信，仅需几条信号线就可实现，如一条发送线、一条接收线及一条地线。
RS-232-C 标准规定的数据传输速率为每秒50,75,100,150,300,600,1200,2400,4800,9600,19200 波特。
一般微机提供标准的RS232C 接口，该接口采用负逻辑，与CMOS、TTL 电路的相连需要专用集成电路进行电平转换。一般应用情况下，RC232C 的最高传输速率为20 kb/s, 最大传输线长为30 米。相比较而言，它的传输速率低、传输距离近、抗共模干扰能力差，在条件较恶劣的现场控制中，很难实现数据的正常传输和获取。
在要求通信距离为几十米到上千米时，广泛采用 RS485 接口。RS485 采用差分接收和驱动，提高抗共模干扰驱动能力，并且提供多点应用，同一线上最多可接32 个驱动器和接收器，最大传输速率10Mb/s(12m)，最大传输距离为1200m（10kb/s），可以较好的实现现场数据的获取和控制。
2. 编程流程
2.1 头文件
2.2 打开串口
2.3 设置串口
核心是设置一个结构：
struct termio
{ unsigned short c_iflag; /* 输入模式标志 */
unsigned short c_oflag; /* 输出模式标志 */
unsigned short c_cflag; /* 控制模式标志*/
unsigned short c_lflag; /* local mode flags */
unsigned char c_line; /* line discipline */
unsigned char c_cc[NCC]; /* control characters */
};
2.4 读写串口
2.5 关闭串口
3. 实例代码
#include termios.h>
#include stdio.h>
#include unistd.h>
#include fcntl.h>
#include sys/signal.h>
#include sys/types.h>
#define BAUDRATE B38400
#define MODEMDEVICE "/dev/ttyS1"
#define _POSIX_SOURCE 1 //POSIX compliant source
#define FALSE 0
#define TRUE 1
volatile int STOP=FALSE;
void signal_handler_IO (int status); //definition of signal handler
int wait_flag=TRUE; //TRUE while no signal received
char devicename[80];
long Baud_Rate = 38400; // default Baud Rate (110 through 38400)
long BAUD; // derived baud rate from command line
long DATABITS;
long STOPBITS;
long PARITYON;
long PARITY;
int Data_Bits = 8; // Number of data bits
int Stop_Bits = 1; // Number of stop bits
int Parity = 0; // Parity as follows:
// 00 = NONE, 01 = Odd, 02 = Even, 03 = Mark, 04 = Space
int Format = 4;
FILE *input;
FILE *output;
int status;
main(int Parm_Count, char *Parms[])
{
char version[80] = " POSIX compliant Communications test program version 1.00 4-25-1999\r\n";
char version1[80] = " Copyright(C) Mark Zehner/Peter Baumann 1999\r\n";
char version2[80] = " This code is based on a DOS based test program by Mark Zehner and a Serial\r\n";
char version3[80] = " Programming POSIX howto by Peter Baumann, integrated by Mark Zehner\r\n";
char version4[80] = " This program allows you to send characters out the specified port by typing\r\n";
char version5[80] = " on the keyboard. Characters typed will be echoed to the console, and \r\n";
char version6[80] = " characters received will be echoed to the console.\r\n";
char version7[80] = " The setup parameters for the device name, receive data format, baud rate\r\n";
char version8[80] = " and other serial port parameters must be entered on the command line \r\n";
char version9[80] = " To see how to do this, just type the name of this program. \r\n";
char version10[80] = " This program is free software; you can redistribute it and/or modify it\r\n";
char version11[80] = " under the terms of the GNU General Public License as published by the \r\n";
char version12[80] = " Free Software Foundation, version 2.\r\n";
char version13[80] = " This program comes with ABSOLUTELY NO WARRANTY.\r\n";
char instr[100] ="\r\nOn the command you must include six items in the following order, they are:\r\n";
char instr1[80] =" 1. The device name Ex: ttyS0 for com1, ttyS1 for com2, etc\r\n";
char instr2[80] =" 2. Baud Rate Ex: 38400 \r\n";
char instr3[80] =" 3. Number of Data Bits Ex: 8 \r\n";
char instr4[80] =" 4. Number of Stop Bits Ex: 0 or 1\r\n";
char instr5[80] =" 5. Parity Ex: 0=none, 1=odd, 2=even\r\n";
char instr6[80] =" 6. Format of data received: 1=hex, 2=dec, 3=hex/asc, 4=dec/asc, 5=asc\r\n";
char instr7[80] =" Example command line: com ttyS0 38400 8 0 0 4 \r\n";
char Param_strings[7][80];
char message[90];
int fd, tty, c, res, i, error;
char In1, Key;
struct termios oldtio, newtio; //place for old and new port settings for serial port
struct termios oldkey, newkey; //place tor old and new port settings for keyboard teletype
struct sigaction saio; //definition of signal action
char buf[255]; //buffer for where data is put
input = fopen("/dev/tty", "r"); //open the terminal keyboard
output = fopen("/dev/tty", "w"); //open the terminal screen
if (!input || !output)
{
fprintf(stderr, "Unable to open /dev/tty\n");
exit(1);
}
error=0;
fputs(version,output); //display the program introduction
fputs(version1,output);
fputs(version2,output);
fputs(version3,output);
fputs(version4,output);
fputs(version5,output);
fputs(version6,output);
fputs(version7,output);
fputs(version8,output);
fputs(version9,output);
fputs(version10,output);
fputs(version11,output);
fputs(version12,output);
fputs(version13,output);
//read the parameters from the command line
if (Parm_Count==7) //if there are the right number of parameters on the command line
{
for (i=1; iParm_Count; i++) // for all wild search parameters
{
strcpy(Param_strings[i-1],Parms);
}
i=sscanf(Param_strings[0],"%s",devicename);
if (i != 1) error=1;
i=sscanf(Param_strings[1],"%li",&Baud_Rate);
if (i != 1) error=1;
i=sscanf(Param_strings[2],"%i",&Data_Bits);
if (i != 1) error=1;
i=sscanf(Param_strings[3],"%i",&Stop_Bits);
if (i != 1) error=1;
i=sscanf(Param_strings[4],"%i",&Parity);
if (i != 1) error=1;
i=sscanf(Param_strings[5],"%i",&Format);
if (i != 1) error=1;
sprintf(message,"Device=%s, Baud=%li\r\n",devicename, Baud_Rate); //output the received setup parameters
fputs(message,output);
sprintf(message,"Data Bits=%i Stop Bits=%i Parity=%i Format=%i\r\n",Data_Bits, Stop_Bits, Parity, Format);
fputs(message,output);
} //end of if param_count==7
if ((Parm_Count==7) && (error==0)) //if the command line entrys were correct
{ //run the program
tty = open("/dev/tty", O_RDWR | O_NOCTTY | O_NONBLOCK); //set the user console port up
tcgetattr(tty,&oldkey); // save current port settings //so commands are interpreted right for this program
// set new port settings for non-canonical input processing //must be NOCTTY
newkey.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
newkey.c_iflag = IGNPAR;
newkey.c_oflag = 0;
newkey.c_lflag = 0; //ICANON;
newkey.c_cc[VMIN]=1;
newkey.c_cc[VTIME]=0;
tcflush(tty, TCIFLUSH);
tcsetattr(tty,TCSANOW,&newkey);
switch (Baud_Rate)
{
case 38400:
default:
BAUD = B38400;
break;
case 19200:
BAUD = B19200;
break;
case 9600:
BAUD = B9600;
break;
case 4800:
BAUD = B4800;
break;
case 2400:
BAUD = B2400;
break;
case 1800:
BAUD = B1800;
break;
case 1200:
BAUD = B1200;
break;
case 600:
BAUD = B600;
break;
case 300:
BAUD = B300;
break;
case 200:
BAUD = B200;
break;
case 150:
BAUD = B150;
break;
case 134:
BAUD = B134;
break;
case 110:
BAUD = B110;
break;
case 75:
BAUD = B75;
break;
case 50:
BAUD = B50;
break;
} //end of switch baud_rate
switch (Data_Bits)
{
case 8:
default:
DATABITS = CS8;
break;
case 7:
DATABITS = CS7;
break;
case 6:
DATABITS = CS6;
break;
case 5:
DATABITS = CS5;
break;
} //end of switch data_bits
switch (Stop_Bits)
{
case 1:
default:
STOPBITS = 0;
break;
case 2:
STOPBITS = CSTOPB;
break;
} //end of switch stop bits
switch (Parity)
{
case 0:
default: //none
PARITYON = 0;
PARITY = 0;
break;
case 1: //odd
PARITYON = PARENB;
PARITY = PARODD;
break;
case 2: //even
PARITYON = PARENB;
PARITY = 0;
break;
} //end of switch parity
//open the device(com port) to be non-blocking (read will return immediately)
fd = open(devicename, O_RDWR | O_NOCTTY | O_NONBLOCK);
if (fd 0)
{
perror(devicename);
exit(-1);
}
//install the serial handler before making the device asynchronous
saio.sa_handler = signal_handler_IO;
sigemptyset(&saio.sa_mask); //saio.sa_mask = 0;
saio.sa_flags = 0;
saio.sa_restorer = NULL;
sigaction(SIGIO,&saio,NULL);
// allow the process to receive SIGIO
fcntl(fd, F_SETOWN, getpid());
// Make the file descriptor asynchronous (the manual page says only
// O_APPEND and O_NONBLOCK, will work with F_SETFL...)
fcntl(fd, F_SETFL, FASYNC);
tcgetattr(fd,&oldtio); // save current port settings
// set new port settings for canonical input processing
newtio.c_cflag = BAUD | CRTSCTS | DATABITS | STOPBITS | PARITYON | PARITY | CLOCAL | CREAD;
newtio.c_iflag = IGNPAR;
newtio.c_oflag = 0;
newtio.c_lflag = 0; //ICANON;
newtio.c_cc[VMIN]=1;
newtio.c_cc[VTIME]=0;
tcflush(fd, TCIFLUSH);
tcsetattr(fd,TCSANOW,&newtio);
// loop while waiting for input. normally we would do something useful here
while (STOP==FALSE)
{
status = fread(&Key,1,1,input);
if (status==1) //if a key was hit
{
switch (Key)
{ /* branch to appropiate key handler */
case 0x1b: /* Esc */
STOP=TRUE;
break;
default:
fputc((int) Key,output);
// sprintf(message,"%x ",Key); //debug
// fputs(message,output);
write(fd,&Key,1); //write 1 byte to the port
break;
} //end of switch key
} //end if a key was hit
// after receiving SIGIO, wait_flag = FALSE, input is available and can be read
if (wait_flag==FALSE) //if input is available
{
res = read(fd,buf,255);
if (res>0)
{
for (i=0; ires; i++) //for all chars in string
{
In1 = buf;
switch (Format)
{
case 1: //hex
sprintf(message,"%x ",In1);
fputs(message,output);
break;
case 2: //decimal
sprintf(message,"%d ",In1);
fputs(message,output);
break;
case 3: //hex and asc
if ((In132) || (In1>125))
{
sprintf(message,"%x",In1);
fputs(message,output);
}
else fputc ((int) In1, output);
break;
case 4: //decimal and asc
default:
if ((In132) || (In1>125))
{
sprintf(message,"%d",In1);
fputs(message,output);
}
else fputc ((int) In1, output);
break;
case 5: //asc
fputc ((int) In1, output);
break;
} //end of switch format
} //end of for all chars in string
} //end if res>0
// buf[res]=0;
// printf(":%s:%d\n", buf, res);
// if (res==1) STOP=TRUE; /* stop loop if only a CR was input */
wait_flag = TRUE; /* wait for new input */
} //end if wait flag == FALSE
} //while stop==FALSE
// restore old port settings
tcsetattr(fd,TCSANOW,&oldtio);
tcsetattr(tty,TCSANOW,&oldkey);
close(tty);
close(fd); //close the com port
} //end if command line entrys were correct
else //give instructions on how to use the command line
{
fputs(instr,output);
fputs(instr1,output);
fputs(instr2,output);
fputs(instr3,output);
fputs(instr4,output);
fputs(instr5,output);
fputs(instr6,output);
fputs(instr7,output);
}
fclose(input);
fclose(output);
} //end of main
/***************************************************************************
* signal handler. sets wait_flag to FALSE, to indicate above loop that *
* characters have been received. *
***************************************************************************/
void signal_handler_IO (int status)
{
// printf("received SIGIO signal.\n");
wait_flag = FALSE;
}
文件:com.tar
大小:3KB
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本文来自ChinaUnix博客，如果查看原文请点：http://blog.chinaunix.net/u1/48467/showart_1867005.html |
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发表于 2009-03-18 10:30