/*
* Serial port driver (uses bit-banging)
* for 16Cxx series parts.
*
* IMPORTANT: Compile this file with FULL optimization
*
* Copyright (C)1996 HI-TECH Software.
* Freely distributable.
*/
#include <htc.h>
/*
* Tunable parameters
*/
/* Xtal frequency */
#define XTAL 4000000
/* Baud rate */
#define BRATE 9600
/* Transmit and Receive port bits */
#define TxData RB6 /* Map TxData to pin */
#define RxData RB7 /* Map RxData to pin */
#define INIT_PORT TRISB = 1<<7 /* set up I/O direction */
/* Don't change anything else */
#define SCALER 10000000
#define ITIME 4*SCALER/XTAL /* Instruction cycle time */
#if BRATE > 1200
#define DLY 3 /* cycles per null loop */
#define TX_OHEAD 13 /* overhead cycles per loop */
#else
#define DLY 9 /* cycles per null loop */
#define TX_OHEAD 14
#endif
#define RX_OHEAD 12 /* receiver overhead per loop */
#define DELAY(ohead) (((SCALER/BRATE)-(ohead*ITIME))/(DLY*ITIME))
void
putch(char c)
{
unsigned char bitno;
#if BRATE > 1200
unsigned char dly;
#else
unsigned int dly;
#endif
INIT_PORT;
TxData = 0; /* start bit */
bitno = 12;
do {
dly = DELAY(TX_OHEAD); /* wait one bit time */
do
/* waiting in delay loop */ ;
while(--dly);
if(c & 1)
TxData = 1;
if(!(c & 1))
TxData = 0;
c = (c >> 1) | 0x80;
} while(--bitno);
NOP();
}
char
getch(void)
{
unsigned char c, bitno;
#if BRATE > 1200
unsigned char dly;
#else
unsigned int dly;
#endif
for(;;) {
while(RxData)
continue; /* wait for start bit */
dly = DELAY(3)/2;
do
/* waiting in delay loop */ ;
while(--dly);
if(RxData)
continue; /* twas just noise */
bitno = 8;
c = 0;
do {
dly = DELAY(RX_OHEAD);
do
/* waiting in delay loop */ ;
while(--dly);
c = (c >> 1) | (RxData << 7);
} while(--bitno);
return c;
}
}
char
getche(void)
{
char c;
putch(c = getch());
return c;
}