/*   A simple RC5 decoder   the demodulator diode is connected to P3.2 (INT0)  and T0 is used to recieve the RC5 bits  The reload values are based on a 12 MHZ XTAL  and on a programmable remote control (EasyTip1 code 718)  This remote control uses a slightly differnd timming  so for standart timming the reload values have to be adjusted  I wrote this because I had to emulate a SAA3049   which is discontinued     more infos and some asm code at:  http://www.ustr.net/infrared/infrared1.shtml  */ #include  "AT892051.h"#define UINT8   unsigned char   #define UINT16  unsigned int    #define UINT32  unsigned long   #define INT8    signed char     #define INT16   signed int      #define INT32   signed long     #define HighB(value) ((value >> 8) & 0xFF)#define LowB(value)  (value & 0xFF)#define RELOAD        -440   // Timming for EasyTip1 Code718 #define FIRST_RELOAD  -870   // and XTAL = 12 MHZ #define _TOGGLE      0x80    // Toggle Bit #define _START2      0x40#define _START1      0x20      typedef struct _BYTE{    UINT8   b3;     /*msb */    UINT8   b2;    UINT8   b1;    UINT8   b0;     /*lsb */}BYTES;typedef union _LONGINT{    UINT32 l;    BYTES  b;}LONGUNION;// global vars bit    bRC5valid;          // 1 after RC5 code was recievedUINT8  command;            // command and subaddress UINT8  subaddress;UINT8  slopecount;         // counter for RC5 slopes LONGUNION shiftreg;        // shiftregister for raw RC5 data//****************************************************************// Interrrupt for reciever diode// this IRQ starts the meassurement Timer //****************************************************************void RC5StartIrq(void) interrupt IE0_VECTOR{   EX0=0;               // disable the IRQ    slopecount=27;       // we need 27 slopes   TH0=HighB(RELOAD);   // first reload    TL0=LowB(RELOAD);   TR0=1;               // start messurement Timer   TF0=0;   ET0=1;               // Timer0 Irq }// **************************************************************// Timerinterrupt, // after 27 slopes the shiftreg contains the RC5 value// und bRC5Valid goes to 1// **************************************************************void TimingIrq(void) interrupt TF0_VECTOR using 1{   bit bLevel;   bLevel= P3_2;            // read level   while (slopecount)       // max 27 slopes   {       TR0=0;                   // T0 stopp       TH0=HighB(FIRST_RELOAD); // new reload value        TL0=LowB (FIRST_RELOAD);       TR0=1;                 // T0 start              if (bLevel)            // add the level to the shift value        {          shiftreg.b.b0=shiftreg.b.b0 | 1;        }       shiftreg.l = shiftreg.l << 1;       slopecount--;       return;          }   TR0=0;             // T0 stop   ET0=0;             // Timer Irq off     bRC5valid=1;       // }//*******************************************************// decodes the recieved value // and sets command and subbaddress // returns 1 if no error occures//         else 0 //*******************************************************bit DecodeRC5Code(void){   UINT8 i;   UINT8 b;   command=0;                                 subaddress=0;   shiftreg.l = shiftreg.l >> 1;   for (i=0; i < 6 ; i ++)                 // first 6 Bit command   {        b=shiftreg.b.b0 & 0x03;      if (b==0x02)           command = command | 0x40;      else if  (b==0x01)         command = command & ~0x40;      else return 0;      command = command >> 1;      shiftreg.l = shiftreg.l >> 2;   }   for (i=0;i < 5;i++)                    // then 5 Bit subaddress   {      b=shiftreg.b.b0 & 0x03;      if (b ==0x02)         subaddress = subaddress | 0x20;      else if (b==0x01)         subaddress = subaddress & ~0x20;      else return 0;        subaddress = subaddress >> 1;      shiftreg.l = shiftreg.l >> 2;   }   b=shiftreg.b.b0 & 0x03;    if (b==0x02)                             // Toggle Bit      command = command |  _TOGGLE;   else if (b==0x01)      command = command & ~_TOGGLE;   else return 0;     shiftreg.l = shiftreg.l >> 2;   b=shiftreg.b.b0 & 0x03;                  // Startbit 2   if (b==0x02)      command = command & ~_START2;         // inverted to command    else if (b==0x01)                        // for extented RC5 (7 Bit Commands)      command = command |  _START2;   else return 0;     shiftreg.l = shiftreg.l >> 2;   b=shiftreg.b.b0 & 0x03;                  // Startbit 1   if (b==0x02)      subaddress = subaddress |  _START1;   else if (b==0x01)      subaddress = subaddress & ~_START1;   else return 0;     return 1;                                // return valid}//*******************************************************// ext.Int0 in slope mode//*******************************************************void InitEx0Irq(void){   EX0=1;          IT0=1;          IE0=0;}//*******************************************************// both timer in 16 Bit mode// T0 is vor RC5 bittime//*******************************************************void InitTimer(void){  TMOD = 0x11;  }void main(void){   InitTimer();   InitEx0Irq();        // ReciverInterupt   shiftreg.l=0x02;     // startvalue    EA=1;   while (1)   {      if (bRC5valid)            // if we got a code      {          bRC5valid=0;          if (DecodeRC5Code())  // then test the shiftreg          {             // here command + subaddress             // has a valid RC5 code          }           shiftreg.l=0x02;      // restart the reciever          IE0=0;          EX0=1;              }   }}