//---------------------------------------------------------------
// EXAMPLE EX2.C :  Basic Template of a C Program with Symbolic
//                  Constants.
//
// 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(). 
//---------------------------------------------------------------
void main()
{
unsigned char X, Y;

outportb(KEY_CON, 0x82);  // Initialize 82C55A PPI with ports 
			  // KEY_PC and KEY_PA as OP ports and 
			  // port PB as an IP port.

X = 0x3F & inportb(KEY_PB);
Y = X ^ 0x0F;
outportb(KEY_PC, Y);
}