/*
FOR EDUCATIONAL PURPOSES ONLY

A TECHNIQUE IS USED THAT IS CONTRARY TO DOCUMENTED INFORMATION BY MICROCHIP
AND SO MAY RESULT IN LEGAL LIABILITY.  IF LEGAL LIABILITY IS A REAL POSSIBILITY
THEN USE ANOTHER APPROACH OR ANOTHER CHIP

Sample C program to demonstrate wake up from sleep of a PIC16F886 with UART
functionality WITHOUT an additional break character. The chip MUST be
configured correctly to use the fast internal oscillator directly and not
as a fall back oscillator.

For simplicity a globally enabled interrupt is NOT used, even though
an individually enabled interrupt is used as wake up source. However
a non demo program  would use an interrupt that has been globally enabled.
All that is required to use a globally enabled interrupt and so interrupt jump 
code is to also set the GIE bit.

Pin RB1 goes low while chip is asleep and goes high chip is awake. 

Demo board used is from the PIC kit Serial Analyzer. Debugger ued is the
PIC kit 2 Debug Express. On the kit RB1 is conencted to LED DS2.

No C libraries used to enhancce portability between C compilers

PICC STD that comes with a CDROM from Microchip will not work for a PIC16F886
Howevere there is a replacement for this compiler from
http://microchip.htsoft.com/products/compilers/piccpro-modes.php

Numerous other compilers should also work. There are plenty to choose from

If using the Serial Analyzer then avoid sending multiple characters as 
simulataneous communication in both directions will occur which the 
Serial Analyzer has problems with. If using the Serial Analyzer with
Hidprobe then Hidprobe will close the port. This problem did not occur 
with an FTDI chip with Hidprobe.

Please note using sleep with a debugger may cause problems requiring reconnects

With this software, Vdd at 3.0 to 5.0 volts and a plain breadboard in use, 
current consumption was measured as low at 0.1 or 0.2 micro amps during sleep.
For this test unused pins were left as outputs and driven low.

Tested at 2400, 57600 and 115200. Both 2400 and 57600 appear to be reliable,
115200 not so.

Default BAUD is now 57600

Power tests with the PICkit serial attached will not be valid

If the receive pin RC7 (pin 18) is left unconnected then chip will not go to sleep
or will keep waking up. If using a breadboard to test power consumption then tie 
this pin high

Two solutions if a serial connection will only be temporary: connect a pull up
resistor or connect also to an input pin which has its weak pull up turned on.

PIC non break uart low power wake up
Version 0.4, 12 January  2009, different BAUD rates tried. Appears reliable up
 to 57600 but not so at 115200
Version 0.3a, 12 January  2009, fix for file not compiling. Programmer loaded 
 previous version and so previous measurments were invalid. Measured power 
 now as expected or better
Version 0.3,  20 December 2008
Version 0.2a, 10 December 2008
Updates to be posted on http://www.zgus.com/pic
Reanme file downloaded from
http://www.zgus.com/pic/pic_breakless_wakeup_c.txt
to pic_breakless_wakeup.c to use in a compiler and IDE

Author: John Heenan, Auscyber Pty Ltd

Copyright 2008 Auscyber Pty Ltd. All rights reserved. 
ZGUS is a trading name of Auscyber Pty Ltd

No Warranty: No warranty of any kind, such as no warranty of fitness 
for any purpose, incsluding no warranty of fitness for merchantability.

No Liability: Auscyber Pty Ltd shall not be liable for any damage or harm 
the software may cause by its use, whether from faults or not, - including 
direct, indirect, incidental, consequential, loss of business profits or special damages

Should you have any questions regarding your right to use this Software,
contact Auscyber Pty Ltd T/A ZGUS at www.zgus.com.

*/

#include <pic.h>//for HTC this uses PIC16f887.h for PIC16f886

//The line below with INTIO is ESSENTIAL to ensure the internal osciallator is chosen straight away
//instead of being chosen as a backup when another specified oscillator fails
//INTIO means internal oscillator with I/O on both OSC1/CLKIN and OSC2/CLKOUT
__CONFIG(INTIO  & WDTDIS & PWRTDIS & MCLREN & UNPROTECT & DUNPROTECT & BORDIS & IESOEN & FCMDIS & LVPDIS & DEBUGEN);
__CONFIG(BORV21 /*& WP0*/);

//#define BAUD 2400
#define BAUD 57600
//#define BAUD 115200
#define FOSC 8000000L //internal oscillator frequency


char rx(void)
{
  char ch=0;
  while(RCIF)//empty the buffer (max 2 characters)
    ch=RCREG;//reading clears RCIF
  if(OERR)//get rid of any overflow error
  {
    CREN=0;
    CREN=1;
  } 
  return ch;
}

void tx(char ch)
{
  while(!TXIF);//wait for TX register to become free
  TXREG=ch;
}

void txputs(const char *str)
{
  const char *p=str;
  char ch;
  while(ch=*p++)
    tx(ch);//or TXREG=ch;
}

volatile char vtemp;//volatile temp to ensure compiler will not optimise away any usage of vtemp

void main(void)
{
 INTCON=0;	//disable interrupts
 IRCF0=1;//change FOSC to 8MHz

//for low power measurements (chip removed from demo board also)
  ANSEL=0;
  ANSELH=0;
  TRISA=0;
  PORTA=0;
  TRISB=0;
  PORTB=0;
  TRISC=0;
  PORTC=0;
  TRISE=0;//for PIC16F887
  PORTE=0;
//RC6=1;TRISC6=0;//in case the UART is reset (such as to clear FERR using SPEN), maintain TX pin high
//also consider connecting RC7 (RX pin) to an input pin with its weak pull up
//turned on (with nRBPU cleared in OPTION register) in case nothing else connected



  BRG16=1;
 #if BAUD==115200
  SPBRG=16;//2.12% error
 #elif BAUD==57600
  SPBRG=34;//-0.79% error
 #elif BAUD<=19200 && BAUD >=300
  SPBRG = (unsigned char)(FOSC/(4 * BAUD) -1); //4 as BRG16=1 and BRGH=1
  SPBRGH= (unsigned char)(((FOSC/(4 * BAUD) -1))>>8);
 #else
  #error "Review BAUD rate calculations"
 #endif
  RCSTA = 0x90;//SREN=1|CREN=1
  TXSTA = 0x24;//TXEN=1|BRGH=1

  TRISB1 = 0;//RB1 is output. skipping RB0 to leave free for external interrupt
//ANS10  = 0;//make RB1 a digital input pin: not required for digital output use
  RB1=1;//pin RB1 set high: not asleep

  RCIE=1;PEIE=1;//ensure an individual interupt will wake up chip even interrupts not globally enabled
//GIE bit is NOT set for simplicty. Interrupts can still wake the chip up though

  txputs("\nPress a key to wake me up from sleep without a break and it will be echoed back");

//FERR errors are not cleared
  while(1)
  {
    if(!RCIF)
    {
      while(!TRMT);//make sure TSR register is empty before shutting oscillator down
      WUE=1;//allow a falling edge or a low to set RCIF early, even while oscillator is off and so wake up chip
      RB1=0;//pin RB1 set low tp show asleep
      asm("sleep");//send chip to sleep by stopping its oscillator
//according to PIC16f886 data sheet, fast oscillaotr is ready in typically less than 10 microceconds
//if nPD of STATUS register is set after a sleep then sleep executed as a NOP due to a posted interrupt
      RB1=1;//pin RB1 set high as not asleep any more
      while(!RCIF);//get rid of early RCIF before character received due to set of WUE
      //while used due to a possible boundary change issue
      vtemp=rx();
      while(!RCIF);//wait for the real RCIF as the wake up character continues
      txputs("\nRB1 low when asleep. Woke up without a break character. Received: ");
      tx(rx());//echo character back
    }
    else
      vtemp=rx();//only process received characters that woke up the chip
  }
}