Gammon Forum

    while(digitalRead(2) == LOW){// ADDEDD
      if (expanderRead (chip1, INFTFA))
        keyValue1 |= expanderRead (chip1, INTCAPA) << 8;    // read value at time of interrupt
      if (expanderRead (chip1, INFTFB))
        keyValue1 |= expanderRead (chip1, INTCAPB);        // port B is in low-order byte
    }

     keyValue1 |= expanderRead (chip1, INTCAPA) << 8;    // read value at time of interrupt
      if (expanderRead (chip1, INFTFB))
     keyValue1 |= expanderRead (chip1, INTCAPB);        // port B is in low-order byte 
// ADDED, attemp to reset the interrupt again
expanderRead (chip1, INTCAPA)
expanderRead (chip1, INTCAPB);

    int count = 0;//just for test
    while(digitalRead(2) == LOW){// ADDEDD
      Serial.print ("count: ");//just for test
      Serial.println (count);//just for test
      if (expanderRead (chip1, INFTFA))
        keyValue1 |= expanderRead (chip1, INTCAPA) << 8;// read value at time of interrupt
      if (expanderRead (chip1, INFTFB))
        keyValue1 |= expanderRead (chip1, INTCAPB); // port B is in low-order byte
      count++;//just for test
    }

// Read port values, as required. Note that this re-arms the interrupts.
  if (expanderRead (INFTFA) || expanderRead (INFTFB))
    {
    keyValue |= expanderRead (INTCAPA) << 8;    // read value at time of interrupt
    keyValue |= expanderRead (INTCAPB);        // port B is in low-order byte
    }

#include <SPI.h>
#include "pins_arduino.h"

// Author: Nick Gammon
// Date: 20 February 2011

// Demonstration of an interrupt service routine connected to the MCP23017

#include <Wire.h>

// MCP23017 registers (everything except direction defaults to 0)
#define SS   53 //I'm using arduinoMega2560
#define IODIRA   0x00   // IO direction  (0 = output, 1 = input (Default))
#define IODIRB   0x01
#define IOPOLA   0x02   // IO polarity   (0 = normal, 1 = inverse)
#define IOPOLB   0x03
#define GPINTENA 0x04   // Interrupt on change (0 = disable, 1 = enable)
#define GPINTENB 0x05
#define DEFVALA  0x06   // Default comparison for interrupt on change (interrupts on opposite)
#define DEFVALB  0x07
#define INTCONA  0x08   // Interrupt control (0 = interrupt on change from previous, 1 = interrupt on change from DEFVAL)
#define INTCONB  0x09
#define IOCON    0x0A   // IO Configuration: bank/mirror/seqop/disslw/haen/odr/intpol/notimp
//#define IOCON 0x0B  // same as 0x0A
#define GPPUA    0x0C   // Pull-up resistor (0 = disabled, 1 = enabled)
#define GPPUB    0x0D
#define INFTFA   0x0E   // Interrupt flag (read only) : (0 = no interrupt, 1 = pin caused interrupt)
#define INFTFB   0x0F
#define INTCAPA  0x10   // Interrupt capture (read only) : value of GPIO at time of last interrupt
#define INTCAPB  0x11
#define GPIOA    0x12   // Port value. Write to change, read to obtain value
#define GPIOB    0x13
#define OLLATA   0x14   // Output latch. Write to latch output.
#define OLLATB   0x15

#define chip1 0x20  // MCP23017 is on I2C address 0x20


volatile boolean keyPressed;

// set register "reg" on expander to "data"
// for example, IO direction
void expanderWriteBoth (const byte address, const byte reg, const byte data ) 
{
  if (SS>0){
    digitalWrite(SS, LOW);
    SPI.transfer (reg);
    SPI.transfer (data);
    SPI.transfer (data);
    digitalWrite(SS, HIGH);
  } 
  else {
    Wire.beginTransmission (address);
    Wire.send (reg);
    Wire.send (data);  // port A
    Wire.send (data);  // port B
    Wire.endTransmission ();
  }
} // end of expanderWrite

// read a byte from the expander
unsigned int expanderRead (const byte address, const byte reg) 
{
  unsigned int data = 0;
  if (SS>0){
    digitalWrite(SS, LOW);
    SPI.transfer (reg);
    digitalWrite(SS, HIGH);
    digitalWrite(SS, LOW);
    data = SPI.transfer (0);
    digitalWrite(SS, HIGH);
  } 
  else {
    Wire.beginTransmission (address);
    Wire.send (reg);
    Wire.endTransmission ();
    Wire.requestFrom (address, (byte) 1);
    data = Wire.receive();
  }
  return data;
} // end of expanderRead

// interrupt service routine, called when pin D2 goes from 1 to 0
void keypress ()
{
  keyPressed = true;   // set flag so main loop knows
}  // end of keypress

void setup ()
{
  Serial.begin (38400); 
  if (SS>0){
    SPI.begin ();
    SPI.setClockDivider(SPI_CLOCK_DIV8);
    digitalWrite(SS, HIGH);
  } 
  else {
    Wire.begin ();
  }

  // expander configuration register
  expanderWriteBoth (chip1, IOCON, 0b01100100); // mirror interrupts, disable sequential mode, open drain

  // enable pull-up on switches
  expanderWriteBoth (chip1, GPPUA, 0xFF);   // pull-up resistor for switch - both ports

  // invert polarity
  expanderWriteBoth (chip1, IOPOLA, 0xFF);  // invert polarity of signal - both ports
 
  // enable all interrupts
  expanderWriteBoth (chip1, GPINTENA, 0xFF); // enable interrupts - both ports
 
  // no interrupt yet
  keyPressed = false;

  // read from interrupt capture ports to clear them
  expanderRead (chip1, INTCAPA);
  expanderRead (chip1, INTCAPB);

  // pin 19 of MCP23017 is plugged into D18 of the ArduinoMega which is interrupt 5
  pinMode (18, INPUT);      // make sure input
  digitalWrite (18, HIGH);  // enable pull-up as we have made the interrupt pins open drain

  attachInterrupt(5, keypress, FALLING);

}  // end of setup

void handleKeypress ()
{
  unsigned int keyValue1 = 0;

  delay (100);  // de-bounce before we re-enable interrupts

  keyPressed = false;

  // check first chip
  if (expanderRead (chip1, INFTFA))
    keyValue1 |= expanderRead (chip1, INTCAPA) << 8;    // read value at time of interrupt
  if (expanderRead (chip1, INFTFB))
    keyValue1 |= expanderRead (chip1, INTCAPB);        // port B is in low-order byte

  // show state of first 16 buttons
  for (byte button = 0; button < 16; button++)
  {
    // this key down?
    if (keyValue1 & (1 << button))
    {
      Serial.print ("Button ");
      Serial.print (button + 1, DEC);
      Serial.println (" now down");
    }  // end of if this bit changed

  } // end of for each button

}  // end of handleKeypress

volatile unsigned long i;

void loop ()
{

  // some important calculations here ...


  // was there an interrupt?
  if (keyPressed)
    handleKeypress ();

}  // end of loop

    digitalWrite(SS, LOW);
    SPI.transfer (reg);
    digitalWrite(SS, HIGH);
    digitalWrite(SS, LOW);
    data = SPI.transfer (0);
    digitalWrite(SS, HIGH);

    digitalWrite(SS, LOW);
    SPI.transfer (reg);
    data = SPI.transfer (0);
    digitalWrite(SS, HIGH);