www.pudn.com > 8255_code_lib.rar > DIOFNC04.C

/*- 
 *  ---------------------------------------------------------------------- 
 *  File        :   DIOFNC04.C 
 *  Creator     :   Blake Miller 
 *  Version     :   01.01.00        February 1991 
 *  Language    :   Microsoft C     Version 5.1 
 *  Purpose     :   Intel 8255 Compatible Digital IO Functions 
 *                  Bit Get Function 
 *  ---------------------------------------------------------------------- 
 *  Revision History: 
 *  022891 BVM  :   Change int to short. 
 *  070490 BVM  :   Creation 
 *  ---------------------------------------------------------------------- 
 */ 
 
#define     DIOFNC04_C_DEFINED  1 
#include    "DIOLIB.H" 
#undef      DIOFNC04_C_DEFINED 
 
void dio_bitget (DIODAT *data, short bit, short *state); 
 
/*- DIO : Bit Get ----------------------------** 
 *  Read one of the bits in the 8255. 
 *  A state of 1 indicates a set bit and a state of 0 
 *  indicates a clear bit. 
 *  The bit number should be from 0 - 23 as follows: 
 *   0 = Port A Bit 0;   7 = Port A Bit 7 
 *   8 = Port B Bit 0;  15 = Port B Bit 7 
 *  16 = Port C Bit 0;  23 = Port C Bit 7 
 *  Passed: 
 *      pointer :   DIODAT 
 *      short   :   bit number 
 *      pointer :   short :   state : 1 = SET, 0 = CLEAR 
 *  Returns: 
 *      nothing 
 *      Loads stat with approrpiate error code. 
 *      Loads state with 0 or 1. 
 */ 
void dio_bitget (DIODAT *data, short bit, short *state) 
	{ 
	short           port;   /* port number  */ 
	unsigned char   ival;   /* in value     */ 
 
	/*  Make sure the bit requested is valid. 
	 *  Three ports of 8 bits each = 24 total bits. 
	 *  This will also validate the port number used later. 
	 */ 
	if ( (bit < 0) || (bit > 23) ){ 
		data->stat = DIO_ST_BB; 
		return; 
		} 
 
	/*  The bit number should have zero offset. 
	 *  This is useful for lining up the port with integer 
	 *  divide and it is also used for left shifting to 
	 *  create a mask. 
	 *  Get port number by doing integer division.  The port 
	 *  number should end up as 0, 1, or 2, corresponding to 
	 *  PORT A, PORT B, and PORT C respectively. 
	 *  Then do modulo 8 to get the corrsponding bit 
	 *  number to be used in the particular byte.  This 
	 *  value will end up being 0 - 7. 
	 */ 
	port = ( bit / 8);      /* port number (0 - 2)          */ 
	bit = bit % 8;          /* modulo to get the bit number */ 
 
	/*  Input data. 
	 *  Right shift data to line it up with the proper bit. 
	 */ 
	dio_bget ( data->base + port, &ival ); 
	ival = ival >> bit;         /* left shift input data    */ 
	ival = ival & 0x01;         /* mask out upper bits      */ 
	*state = (short) ival;      /* load value               */ 
 
	data->stat = DIO_ST_OK; 
	} 
 
/*- 
 *  ---------------------------------------------------------------------- 
 *  END DIOFNC04.C Source File 
 *  ---------------------------------------------------------------------- 
 */