serial.c

来自「这是PIC驱动程序源码」· C语言 代码 · 共 93 行

/*
 *	Serial port driver for 16Cxx chips
 *	using software delays.
 *
 *	Copyright (C)1996 HI-TECH Software.
 *	Freely distributable.
 */

/*
 *	Tunable parameters
 */

#include	<pic.h>
#include	<conio.h>

/*	Transmit and Receive port bits */

static bit	TxData @ (unsigned)&PORTA*8+3;		/* bit3 in port A */
static bit	RxData @ (unsigned)&PORTA*8+2;		/* bit2 in port A */
#define	INIT_PORT	TRISA = 7			/* set up I/O direction */

/*	Xtal frequency */

#define	XTAL	4000000

/*	Baud rate	*/

#define	BRATE	9600

/*	Don't change anything else */

#define	DLY		3		/* cycles per null loop */
#define	TX_OHEAD	13		/* overhead cycles per loop */
#define	RX_OHEAD	12		/* receiver overhead per loop */

#define	DELAY(ohead)	(((XTAL/4/BRATE)-(ohead))/DLY)

void
putch(char c)
{
	unsigned char	dly, bitno;

	bitno = 11;

	INIT_PORT;
	TxData = 0;			/* start bit */
	bitno = 12;
	do {
		dly = DELAY(TX_OHEAD);	/* wait one bit time */
		do
			/* nix */ ;
		while(--dly);
		if(c & 1)
			TxData = 1;
		if(!(c & 1))
			TxData = 0;
		c = (c >> 1) | 0x80;
	} while(--bitno);
}

char
getch(void)
{
	unsigned char	c, bitno, dly;

	for(;;) {
		while(RxData)
			continue;	/* wait for start bit */
		dly = DELAY(3)/2;
		do
			/* nix */;
		while(--dly);
		if(RxData)
			continue;	/* twas just noise */
		bitno = 8;
		c = 0;
		do {
			dly = DELAY(RX_OHEAD);
			do
				/* nix */;
			while(--dly);
			c = (c >> 1) | (RxData << 7);
		} while(--bitno);
		return c;
	}
}