My note for pascalio/test/mcp23017_i2cdev/project1.lpr file

{

   I have connected one of the pin of PortA to one of the pin on PortB.

   Therefore, when one pin from portA is "ON" as output,

   the other pin from PortB should be "ON" for input.

}

program project1;
 
{$mode objfpc}{$H+}
 
uses
  sysutils,
  pascalio, fpi2c
  { you can add units after this };
 
var
  idev: TI2CLinuxDevice;
  bval, b: Byte;
begin
  idev := nil;
  try
    idev := TI2CLinuxDevice.Create($20, 1);
    writeln('Device file handle: ', idev.Handle);
    bval := idev.ReadRegByte($12);
    Writeln('Register $12 (GPIOA): ', binstr(bval,8));
 
    idev.WriteRegByte($01, $00); // GPIOB = Output
    for bval := 0 to 5 do
    begin
      idev.WriteRegByte($13, $FF);
      b := idev.ReadRegByte($12);
      Writeln('Register $12 (GPIOA): ', binstr(b,8));
      Sleep(1000);

      idev.WriteRegByte($13, $00);
      b := idev.ReadRegByte($12);
      Writeln('Register $12 (GPIOA): ', binstr(b,8));
      Sleep(1000);
    end;
  except
    // this exception handling should be a try/finally block
    // but FPC 2.7.1 doesn't do the default exception handling
    // so this is workaround to avoid memory leaking the exception object
    on e: exception do // Error Handling
    begin
      writeln(ErrOutput, 'E Class  : ', e.ClassName);
      writeln(ErrOutput, 'E Message: ', e.Message);
      writeln(ErrOutput, 'E Address: ', hexStr(ExceptAddr));
    end;
  end;
  idev.Free;
end.