Hi!
Days ago, I posted a query about bioscom() function in c++[turbo c], in reference with serial port programming. Though I was unable to get through with that problem but instead found outportb(), inportb() functions in c for the same purpose.
Following are the serial port settings which I copy pasted into my code and it worked. Now I want to understand these settings (i.e. the code)...
Please help me.

#define PORT1 0x3F8
outportb(PORT1 + 1 , 0);
outportb(PORT1 + 3 , 0x80);
outportb(PORT1 + 0 , 0x0c);
outportb(PORT1 + 1 , 0x00);
outportb(PORT1 + 3 , 0x03);
outportb(PORT1 + 2 , 0xC7);
outportb(PORT1 + 4 , 0x0B);

 

Hi!
Days ago, I posted a query about bioscom() function in c++[turbo c], in reference with serial port programming. Though I was unable to get through with that problem but instead found outportb(), inportb() functions in c for the same purpose.
Following are the serial port settings which I copy pasted into my code and it worked. Now I want to understand these settings (i.e. the code)...
Please help me.

#define PORT1 0x3F8
outportb(PORT1 + 1 , 0);
outportb(PORT1 + 3 , 0x80);
outportb(PORT1 + 0 , 0x0c);
outportb(PORT1 + 1 , 0x00);
outportb(PORT1 + 3 , 0x03);
outportb(PORT1 + 2 , 0xC7);
outportb(PORT1 + 4 , 0x0B);

This code writes bytes of data to five serial ports: 0x3F8, 0x3F9, 0x3FA, 0x3FB, and 0x3FC.

I found the same code as above on the internet, with comments, so that might help you understand the purpose of each line of code above. Here's a link to where this code appears: http://www.tek-tips.com/viewthread.cfm?qid=624898.

/* This program is used to pull data from the serial port */

#include <dos.h>
#include <stdio.h>
#include <conio.h>

#define PORT1 0x3F8  /* Defines Serial Port Base Address (COM1 */

void main(void){
    unsigned char c = 0;
    unsigned char chrctr = 0;
    /*int exit = 1; */

    outportb(PORT1 + 1, 0); /* Turn off interrupts */

    /* PORT1 Communication Settings */

    outportb(PORT1 + 3, 0x80); /* Set DLAB ON */
    outportb(PORT1 + 0, 0x0C); /* Set the baud rate to 9600 */

    outportb(PORT1 + 1, 0x00); /* Set Baud - Divisor latch HIGH */
    outportb(PORT1 + 3, 0x03); /* 8 bits, no parity, 1 stop */
    outportb(PORT1 + 2, 0xC7); /* FIFO Control Register */
    outportb(PORT1 + 4, 0x0B); /* Turn on DTR, RTS, and OUT2) */

 

It looks like there is a UART chip like an 8250 or 16550 located at that base address, and these port writes are writing directly to the chip registers.

If you want to dig deeper into the meaning of each command, read about the chip itself:

http://www.national.com/ds/PC/PC16550D.pdf

For a more user-friendly introduction to programming this chip, also see:

http://en.wikibooks.org/wiki/Serial_Programming/8250_UART_Programming