PIC Micro Controller C Input / Output Routine

Quadrature Encoder ISR

by David Kott

struct RotaryEncoderStruct {
      int unused:4;  // RB[0:3]
      int A:1;   // RB4
      int B:1;   // RB5
      int unused2:2;  // RB6-7
};

struct RotaryEncoderStruct RotaryEncoder;

#pragma BYTE PORTB = 0x06

#pragma BYTE RotaryEncoder = 0x06 // Place structure right over PORTB at
location 0x06


USHORT g_usEncoderCount = 0;

#pragma INT_RB
void
PortBInterrupt (void)
{

      static BYTE OldPortB;
      BYTE byTemp;
      static struct RotaryEncoderStruct OldEncoder;


      if (OldPortB != (byTemp=(PORTB & 0x30))) {


      OldPortB = byTemp;

      if (RotaryEncoder.A == OldEncoder.A) {
     if (RotaryEncoder.B == RotaryEncoder.A)
    --g_usEncoderCount;
     else
    ++g_usEncoderCount;
      } else {
     OldEncoder.A = RotaryEncoder.A;
     if (RotaryEncoder.B == RotaryEncoder.A)
    ++g_usEncoderCount;
     else
    --g_usEncoderCount;
      }



     }

   // Handle more PORTB stuff here, like a button, or something.


}

Questions:

• Ken T Macfarlane of p.s. autogrinding asks:

  How many machine cycles does this take to run (worst case)? This sets the maximum rotational speed of encoder that can be tracked (tempered by the processor clock speed and the encoder resolution in lines/rev, obviously)

  +

Comments:

• karl.ratcliff at TakeThisOuTtiscali.co.uk " Doesn't check for overrun or error conditions. The output of the encoder will be gray code changing by one bit, so a two bit change = error condition" +

See also:

PICList 2013 contributors: o List host: MIT, Site host massmind.org, Top posters @20130519 RussellMc, IVP, John Gardner, veegee, Bob Blick, alan.b.pearce, Sean Breheny, Josh Koffman, Carl Denk, Isaac Marino Bavaresco, * Page Editors: James Newton, David Cary, and YOU! * Roman Black of Black Robotics donates from sales of Linistep stepper controller kits. * Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters. * Monthly Subscribers: None at this time. on-going support is MOST appreciated! * Contributors: Richard Seriani, Sr.

  .