//---------------------------------------------------------------
// EXAMPLE EX17.C :  Demonstrate use of a UNION and STRUCTURE.
//
// C.P. Diduch, Dec 1999.
//---------------------------------------------------------------
#define	KEY_PA	0x138	  // 82C55A port addresses for PA,
#define KEY_PB	0x13A	  // PB,
#define KEY_PC	0x13C	  // PC and the
#define KEY_CON	0x13E	  // Control Register.

#include <conio.h> 	  // conio.h contains prototypes for 
			  // inportb() and outportb(). 
//---------------------------------------------------------------
union IO {
   struct {
	 char LSB;
	 char MSB;
	 } ABYTE;
   int AWORD;
   };
//---------------------------------------------------------------
void main()
{
union IO Y;	// Y is a variable that may be accessed as a word
		// (16-bits) by Y.AWORD. The high and low bytes 
		// that comprise Y may be accessed as Y.ABYTE.LSB
		// and Y.ABYTE.MSB !
unsigned X;

outportb(KEY_CON, 0x82);  // Initialize 82C55A PPI with ports 
			  // KEY_PC and KEY_PA as OP ports and 
			  // port PB as an IP port.
for (X = 0; X < 256; X++) {
-   Y.AWORD = X * X;
   outportb(KEY_PA, Y.ABYTE.LSB);
   outportb(KEY_PC, Y.ABYTE.MSB);
   }
}