/*
 * 9 bit BitBang Serial routines
 * 19/Dec/1999 JLS
 * (c) 1999 Jose Luiz Pinto Souto
 * souto@cryogen.com
 * CC5x Compiler (www.bknd.com)
 * 10 MHz operation
 */

#include	<16f84.h>

#pragma update_RP 0   /* OFF */

#define DEF_TRISA	0x00
#define DEF_TRISB	0x01

bit 	_TxOUT		@ PORTA.0;
bit	RxD_pin		@ PORTB.0;


unsigned char rxBuf[2];

void Delay_uSeg (unsigned char timeout);
void TxSerial (void);
void RxSerial (void);

/*--------------------------------------------------------------------------*/
void Delay_uSeg (unsigned char timeout) {
/*--------------------------------------------------------------------------*/

	// delay = (3*timeout + 7) * 0.4uS (including call and return)

	while (1) {
		timeout--;
		if (timeout==0) {
			nop();
			nop();
			return;
		}
	}

}// Delay_uSeg

/*--------------------------------------------------------------------------*/
void TxSerial (void) {
/*--------------------------------------------------------------------------*/

/*
 ;---------------------------------------------------------------------------*
 ; Transmit 1 start bit Lo, 9 data bits and 1 stop bit Hi at 9600 bps
 ; Byte time = 1.144 mS
 ; Bit  time = 104 uS (0.16% error @ 10 MHz)
 ; Input : rxBuf[0] = 9th bit (bit 0)
 ;         rxBuf[1] = byte to be transmitted
 ; Output: byte transmitted by serial pin
 ;---------------------------------------------------------------------------*
*/

	char idx;

	rxBuf[0] = rxBuf[0] | 0x02;		// stop bit added
	Carry = 0;				// start bit in carry

	for (idx=11; idx; idx--) {		// 3*0.4us=1.2us
		_TxOUT = Carry;			// 4*0.4us=1.6us
		Delay_uSeg(80);			// (80*3+7)*0.4us = 98.8 us
		rxBuf[0]  = rr(rxBuf[0]);	// 1*0.4us=0.4us
		rxBuf[1]  = rr(rxBuf[1]);	// 1*0.4us=0.4us
	}					// 3*0.4us=1.2us
}

/*--------------------------------------------------------------------------*/
void RxSerial (void) {
/*--------------------------------------------------------------------------*/

/*
 ;---------------------------------------------------------------------------*
 ; Receives 1 start bit Lo, 9 data bits and 1 stop bit Hi at 9600 bps
 ; Byte time = 1.144 mS
 ; Bit  time = 104 uS (0.16% erro w/10 Mhz)
 ;
 ; False start bit check
 ;
 ; Start bit hunting timeout = 4*1.283ms 
 ;
 ; Input  : none
 ; Output : Carry = 1 => success
 ; 	    rxBuf[0,1] = input byte +9th bit
 ; 	    Carry = 0 => error (timeout or stop bit=0)
 ;---------------------------------------------------------------------------*
*/

	char idx;

	rxBuf[0] = 4;				// 5.135 ms timeout
	idx      = 0;

	while (1)
	{
		while (RxD_pin)			// input "high"
		{
			if ((-- idx)==0)
			{
				rxBuf[0]--;
				if (rxBuf[0]==0)
				{
					Carry = 0;
					return;
				}
			}
		}

		Delay_uSeg(40);			// 1/2 bit delay (40*3+7)*0.4us=50.8us
		if (RxD_pin)
			continue;		// false start bit detection

		rxBuf[0] = 0x01;		// 9 bits counter and reception buffer
		rxBuf[1] = 0x00;

		do
		{
			Delay_uSeg(81);			// (81*3+7)*0.4us=100us
			nop();				// 0.4us
			nop();				// 0.4us
			Carry = RxD_pin;		// 1.2us bit read
			rxBuf[0] = rr(rxBuf[0]);	// 0.4us store and count
			rxBuf[1] = rr(rxBuf[1]);	// 0.4us
		}					// 1.2us
		while (Carry==0);
		Delay_uSeg(81);			// (81*3+7)*0.4us=100us
		nop();				// 0.4us
		Carry = RxD_pin;		// stop bit read
		return;				// 100 us availiable
	}
}


/*--------------------------------------------------------------------------*/
void main (void)
/*--------------------------------------------------------------------------*/
{

	INTCON	= 0;					// no interrupts
	PCLATH	= 0;					// bank 0
	PORTA	= 1;
	PORTB	= 0;
	RP0	= 1;					// RAM bank 1
	TRISA	= DEF_TRISA;
	TRISB	= DEF_TRISB;
	OPTION  = 0b11000011;				// Prescaler Timer0 1:16
	RP0	= 0;					// RAM bank 0

	while (1) {
//		RxSerial();
		rxBuf[0]=0x01;				// 9th bit
		rxBuf[1]=0xAA;				// test byte
		TxSerial();
	}

}