（2）使用查詢方法的串行通訊程序設(shè)計：

#include
#include
#include
#define PortBase 0x2F8

void com_putch(unsigned char);
int com_chkch(void);

main()
{
int c;
unsigned char ch;

outportb(PortBase + 1 , 0); /* Turn off interrupts - Port1 */

/* Set COM1: 9600,8,N,1*/
outportb(PortBase + 3 , 0x80);
outportb(PortBase + 0 , 0x0C);
outportb(PortBase + 1 , 0x00);
outportb(PortBase + 3 , 0x03);

clrscr();

while(1) {

c = com_chkch();
if(c!=-1) {
c &= 0xff; putch(c);
if(c==n) putch(r);
}

if(kbhit()) {
ch = getch(); com_putch(ch);
}
}

}


void com_putch(unsigned char ch) {
unsigned char status;

while(1) {
status = inportb(PortBase+5);
if(status&0x01) inportb(PortBase+0); else break;
}

outportb(PortBase,ch);
}

int com_chkch(void) {
unsigned char status;

status = inportb(PortBase+5);
status &= 0x01;
if(status) return((int)inportb(PortBase+0)); else return(-1);

}

使用查詢方式的通訊程序適合9600bps以下的應(yīng)用。

（3）使用中斷的串行通訊程序設(shè)計：

該程序由兩部分組成，serial.c及sercom.c，sercom.c為通訊的底層驅(qū)動，使用中斷的串行通訊程序可以工作到115.2Kbps.

#include
#include
#include
#include
#include
#include "llio.c"

COM *c;

main()
{
unsigned char ch;

c = ser_init( PORT_B,BAUD_9600,_COM_CHR8,_COM_NOPARITY,4096,4096 );

while(1) {

if( serhit(c)) {
ch = getser(c);
putchar(ch);
}

if(kbhit()) {
ch = getch();
putser(ch,c);
}

}
}

#include
#include
#include
#include

#define CR 0x0d
#define TRUE 0xff
#define FALSE 0

#define PORT_A 0 /* COM1 */
#define PORT_B 1 /* COM2 */
#define BAUD_9600 _COM_9600
#define BAUD_4800 _COM_4800
#define BAUD_2400 _COM_2400
#define BAUD_1200 _COM_1200
#define BAUD_600 _COM_600
#define BAUD_300 _COM_300
#define BAUD_110 _COM_110


typedef struct {
char ready; /* TRUE when ready */
unsigned com_base; /* 8250 Base Address */
char irq_mask; /* IRQ Enable Mask */
char irq_eoi; /* EOI reply for this port */
char int_number; /* Interrupt # used */
void (_interrupt _far *old)( void ); /* Old Interrupt */

/* Buffers for I/O */

char *in_buf; /* Input buffer */
int in_tail; /* Input buffer TAIL ptr */
int in_head; /* Input buffer HEAD ptr */
int in_size; /* Input buffer size */
int in_crcnt; /* Input count */
char in_mt; /* Input buffer FLAG */

char *out_buf; /* Output buffer */
int out_tail; /* Output buffer TAIL ptr */
int out_head; /* Output buffer HEAD ptr */
int out_size; /* Output buffer size */
char out_full; /* Output buffer FLAG */
char out_mt; /* Output buffer MT */
} COM;


COM *ser_init( int port,int baud,int bit,int parity,int isize,int osize );
void ser_close( COM *c );


int getsers( COM *c,int len,char *str );
int putsers( char *str, COM *c );
char serline( COM *c );
int getser( COM *c );
char serhit(COM *c);
char putser(char outch,COM *c);
void cntl_rts(int flag,COM *c);
void cntl_dtr(int flag,COM *c);
void clean_ser( COM *c );


#define COM1_BASE 0x03F8
#define COM1_IRQ_MASK 0xEF /*11101111B IRQ 4 For COM1 */
#define COM1_IRQ_EOI 0x64 /* IRQ 4 Spec EOI */
#define COM1_INT_NUM 0x0C /* Int # for IRQ4 */

#define COM2_BASE 0x02F8
#define COM2_IRQ_MASK 0xF7 /*11110111B IRQ 3 For COM2 */
#define COM2_IRQ_EOI 0x63 /* IRQ 3 Spec EOI */
#define COM2_INT_NUM 0x0B /* Int # for IRQ3 */

/* 8250 ACE register defs */

#define THR 0 /* Offset to Xmit hld reg (write) */
#define RBR 0 /* Receiver holding buffer (read) */
#define IER 1 /* Interrupt enable register */
#define IIR 2 /* Interrupt identification reg */
#define LCR 3 /* Line control register */
#define MCR 4 /* Modem control register */
#define LSR 5 /* Line status register */
#define MSR 6 /* Modem status register */

#define SREG(x) ((unsigned)((unsigned)x + c->com_base))

/* 8259 Int controller registers */

#define INTC_MASK 0x21 /* Interrupt controller MASK reg */
#define INTC_EOI 0x20 /* Interrupt controller EOI reg */


#define MAX_PORTS 2 /* # I/O ports (DOS limit) */
static int count = 0;
static COM com_list[MAX_PORTS]; /* I/O data structure */

static COM *com1; /* Pointers for interrupt actions */
static COM *com2;
static COM *com_xfer; /* Transfer interrupt data structure */

COM *ser_init0(int port,char *ibuf,int isize, char *obuf,int osize);
void ser_close0( COM *c );


void (_interrupt _far int_ser1)( void ); /* Int rtn for serial I/O COM 1 */
void (_interrupt _far int_ser2)( void ); /* Int rtn for serial I/O COM 2 */
void (_interrupt _far int_ser_sup)( void ); /* Support int actions */

COM *ser_init( int port,int baud,int bit,int parity,int isize,int osize )
{
unsigned status;
char ch;
COM *c;
char *in_buf,*out_buf;

status = _bios_serialcom(_COM_INIT,port,(bit | parity | _COM_STOP2| baud ));


in_buf = malloc( isize );
if( in_buf == NULL ) return( NULL );

out_buf = malloc( osize );
if( out_buf == NULL ) return( NULL );

c = ser_init0(port,in_buf,isize,out_buf,osize );

clean_ser(c);

return( c );
}


void ser_close(COM *c)
{
int i;


if( !c->ready ) return;

ser_close0(c);

free( c->in_buf );
free( c->out_buf );

}


char serline( COM *c )
{

if( !c->ready ) return(FALSE);

if( c->in_crcnt > 0 ) return( TRUE );
else return( FALSE );
}

int getsers( COM *c,int len,char *str )
{
char ch;
int i;

i = 0;
while( i while( !serhit(c) ) {
if(kbhit()) return( -1 );
}

ch = 0x7f & getser(c);
switch( ch ) {

case 0x0d: str[i++] =