EX_ENCOD.C
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/////////////////////////////////////////////////////////////////////////
//// EX_ENCODE.C ////
//// ////
//// This program connects to a 2 bit optical encoder. The encoder ////
//// input is on pins A0 and A1. A number is input on port B. ////
//// The software will output a square wave on pin A3 representing ////
//// the encoder RPM divided by the number on port B. If there ////
//// is an error from the encoder pin A2 is made high. ////
//// ////
//// This example will work with the PCB, PCM and PCH compilers. ////
//// The following conditional compilation lines are used to ////
//// include a valid device for each compiler. Change the device, ////
//// clock and RS232 pins for your hardware if needed. ////
/////////////////////////////////////////////////////////////////////////
//// (C) Copyright 1996,2001 Custom Computer Services ////
//// This source code may only be used by licensed users of the CCS ////
//// C compiler. This source code may only be distributed to other ////
//// licensed users of the CCS C compiler. No other use, ////
//// reproduction or distribution is permitted without written ////
//// permission. Derivative programs created using this software ////
//// in object code form are not restricted in any way. ////
/////////////////////////////////////////////////////////////////////////
#if defined(__PCM__)
#include <16c64.h>
#fuses HS,NOWDT,NOPROTECT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7) // Jumpers: 8 to 11, 7 to 1
#elif defined(__PCB__)
#include <16c56.h>
#fuses HS,NOWDT,NOPROTECT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_A3, rcv=PIN_A2) // Jumpers: 11 to 17, 12 to 18
#elif defined(__PCH__)
#include <18c452.h>
#fuses HS,NOPROTECT
#use delay(clock=20000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7) // Jumpers: 8 to 11, 7 to 12
#endif
byte const sequence[4] = {0,2,3,1};
byte seq_index;
byte error_count;
void resync() {
int value;
if(error_count==4)
output_high(pin_a2);
else
error_count++;
value=input_a() & 3;
if(value==sequence[0])
seq_index=0;
else if (value==sequence[1])
seq_index=1;
else if (value==sequence[2])
seq_index=2;
else if (value==sequence[3])
seq_index=3;
}
main() {
short output;
long count,max_count;
error_count=0;
resync();
do {
while((input_a() & 3)==sequence[seq_index]) ;
seq_index=(seq_index+1)&3;
if ((input_a() & 3)!=sequence[seq_index])
resync();
else {
if(error_count==0)
output_low(pin_a2);
else
--error_count;
max_count=input_b()>>2;
count++;
if(count>max_count) {
output=!output;
output_bit(pin_a3,output);
count=0;
}
}
} while (true);
}
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