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/*
W. Strobl, Bonn, March 2014
Simple minded software bit banging async RS232 implementation for Microchip XC8
http://en.wikipedia.org/wiki/Bit_banging
Tested with 2400, 9600 and 19200 baud on a 4 MHz 16F675 so far
Tested with 9600 baud on a 32 MHz 12F1840.
19200 softuard doesn't work.
PIC12F1840
___ __
10k -|___|-+ Vdd -o| o|o- Vss
___ +-RS232in / GP5 -o| |o- GP0 / ICSPDAT
1k -|___|-- RS232out/ GP4 -o| |o- GP1 / ICSPCLK
Vpp / GP3 -o|__|o- GP2 /
Necessary definitions (examples)
#define FCY 1000000 // cycles per second (4 MHz PIC)
#define SOFTUART_RXPIN GPIO5 // if input is desired
#define SOFTUART_TXPIN GPIO4 // if output is desired
Optional definitions
#define SOFTUART_BAUD 19200 // default: 9600
#define SOFTUART_STDIO 1 // if definition for getch, putch is desired
// default: 0
#define SOFTUART_DI 1 // if interrupts are to be disabled during IO
// default: 0
#define SOFTUART_MARK 0 // 0: not inverted (default: 1)
Typical:
#define SOFTUART_RXPIN GPIO5
#define SOFTUART_TXPIN GPIO4
#define SOFTUART_STDIO 1
#define SOFTUART_DI 1
#include "softuart.h"
#define kbhit softuartkbhit
*/
/******************************************************************************/
// Software UART
/******************************************************************************/
// FCY == instructions per second, see system.h for xc8
#ifndef SOFTUART_BAUD // default baudrate
#define SOFTUART_BAUD 9600
#endif
#define SOFTUART_BITLEN (FCY/SOFTUART_BAUD)
#define SOFTUART_DELAY (SOFTUART_BITLEN/5)
#ifndef SOFTUART_MARK
#define SOFTUART_MARK 1 // 0: not inverted (default: 1)
#endif
// Input Pin defined?
#ifdef SOFTUART_RXPIN
/******************************************************************************/
// Input
/******************************************************************************/
char softuartgetch(void)
{
char rcvd,i;
#if SOFTUART_DI
di();
#endif
rcvd=0;
_delay(SOFTUART_BITLEN/2-10); // wait half a startbit
if (SOFTUART_RXPIN != SOFTUART_MARK)
{
#if SOFTUART_DI
ei();
#endif
return 0; // glitch
}
_delay(SOFTUART_BITLEN/2-10); // wait half a startbit
for (i=0;i<8;i++)
{
rcvd >>= 1; // shift previous bits, LSB comes first
_delay(SOFTUART_BITLEN/2-12); // ADJUST
rcvd |= ((SOFTUART_RXPIN != SOFTUART_MARK)?0x80:0);
_delay(SOFTUART_BITLEN/2-10); // ADJUST
}
#ifdef SOFTUART_DI
ei();
#endif
_delay(SOFTUART_BITLEN); // stopbit
return rcvd;
}
#define softuartkbhit() (SOFTUART_RXPIN == SOFTUART_MARK)
#endif
// Output Pin defined?
#ifdef SOFTUART_TXPIN
/******************************************************************************/
// Output
//******************************************************************************/
#if defined(SOFTUART_TXPIN) || defined(SOFTUART_STDIO)
#define softuartputch putch
#endif
void softuartputch(char c)
{
char i;
#ifdef SOFTUART_DI
di();
#endif
SOFTUART_TXPIN = SOFTUART_MARK; // startbit
_delay(SOFTUART_BITLEN-20); // Adjust Schleifeninit braucht
for (i=0;i<8;i++)
{
SOFTUART_TXPIN = c; // checken, ob da das untere Bit verwendet wird sonst
#if SOFTUART_MARK
SOFTUART_TXPIN = ~(c&1);
#else
SOFTUART_TXPIN = c&1;
#endif
c >>=1;
_delay(SOFTUART_BITLEN-20); // Adjust
}
SOFTUART_TXPIN = ~SOFTUART_MARK;
_delay(SOFTUART_BITLEN*2); // two stop bits
#ifdef SOFTUART_DI
ei();
#endif
}
#endif
/******************************************************************************/
// Utility
/******************************************************************************/
#if defined(SOFTUART_RXPIN) || defined(SOFTUART_STDIO)
// getch with wait
char getch(void)
{
while (!softuartkbhit()) _delay(1);
return softuartgetch();
}
#endif
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