RS-232 is one of the most common communication interfaces found in personal computers, designed as an asynchronous serial communication standard by the Electronic Industries Association (EIA). It typically comes in two forms: a 9-pin connector (DB-9) or a 25-pin connector (DB-25). Most PCs are equipped with at least two RS-232 ports, usually labeled as COM1 and COM2, allowing for serial communication with external devices.
In serial communication, both the transmitting and receiving devices must use a standardized interface to ensure compatibility. The RS-232-C standard, often referred to simply as RS-232, is the most widely used interface for serial data transfer. The "-C" in "RS-232-C" denotes a specific revision of the standard, but it is commonly used interchangeably with just "RS-232."
Originally developed in 1970 by the EIA in collaboration with Bell Systems, modem manufacturers, and computer terminal producers, the RS-232 standard was created to define the electrical and functional characteristics of the interface between data terminal equipment (DTE) and data communication equipment (DCE). The original specification defined a 25-pin DB-25 connector, with detailed signal definitions and voltage levels. However, IBM later simplified this to a 9-pin DB-9 connector, which became the de facto standard for many PC applications. In industrial control systems, only three lines—RXD (receive data), TXD (transmit data), and GND (ground)—are typically used.
**RS-232 Serial Communication Program**
```c
#include
#include "stdio.h"
#include
main()
{
char ch;
/************************Serial port initialization***********************/
outportb(0x3fb, 0x80); // Set LCR, access DLL/DLM, disable interrupt, no parity, 1 stop bit
outportb(0x3f8, 0x0C); // Set baud rate low byte (DLL)
outportb(0x3f9, 0x00); // Set baud rate high byte (DLM)
outportb(0x3fb, 0x03); // Set LCR, disable DLL/DLM access, no parity, 1 stop bit
outportb(0x3fc, 0x03); // Initialize MCR, DTR and RTS enabled
while(1) // Keep listening state
{
/*************************Send data***********************/
if(bioskey(1))
{
ch = bioskey(0) & 0x0ff; // Get ASCII code from keyboard input
if(ch == 27) // If 'ESC' key is pressed, exit program
exit(0);
outportb(0x3f8, ch); // Send character to the transmit buffer
}
/*************************Receive data***********************/
ch = inportb(0x3fd); // Read line status register (LSR)
if(ch & 0x01) // If bit 0 is set, data is ready to be read
{
ch = inportb(0x3f8); // Read received data
printf("%c", ch); // Display received character
}
}
}
```
Note: The base address for COM1 is 0x3F8, and for COM2 it is 0x2F8. Depending on your serial cable setup, you should choose the appropriate COM port for communication. This simple program demonstrates basic RS-232 serial communication, including sending and receiving characters through the console.
Jiangsu Qilong Electronic Technology Co., Ltd. , https://www.qilongtouch.com