www.pudn.com > 8255_code_lib.rar > I8255F09.C

/*- 
 *  ---------------------------------------------------------------------- 
 *  File        :   I8255F08.C 
 *  Creator     :   Blake Miller 
 *  Version     :   01.00.00        February 1991 
 *  Language    :   Microsoft C     Version 5.1 
 *  Purpose     :   Intel 8255 Compatible Digital IO Functions 
 *              :   Toggle Output Bit Function 
 *  ---------------------------------------------------------------------- 
 */ 
 
#define  I8255F08_C_DEFINED  1 
#include "I8255FN.H" 
#undef   I8255F08_C_DEFINED 
 
void I8255_bittog (I8255DAT *data, int bit); 
 
/*- I8255 : Toggle Output Bit ----------------** 
 *  Toggle one of the output bits in the 8255. 
 *  The bit state is toggled. 
 *  The bit number should be from 1 - 24 as follows: 
 *   1 = Port A Bit 0;   8 = Port A Bit 7 
 *   9 = Port B Bit 0;  16 = Port B Bit 7 
 *  17 = Port C Bit 0;  24 = Port C Bit 7 
 *  Note: 
 *  0 XOR 0 = 0; 1 XOR 0 = 1 => Do not affect other bits. 
 *  0 XOR 1 = 1; 1 XOR 1 = 0 => Affect toggle bit. 
 *  Passed: 
 *      pointer :   I8255DAT 
 *      integer :   bit number 
 *  Returns: 
 *      nothing 
 *      Loads stat with appropriate error code 
 */ 
void I8255_bittog (I8255DAT *data, int bit) 
	{ 
	int             port;   /* port number  */ 
	int             padd;   /* port address */ 
	unsigned char   mask;   /* byte mask    */ 
	unsigned char   oval;   /* out value    */ 
 
	/*  Make sure the bit requested is valid. 
	 *  Three ports of 8 bits each = 24 bits. 
	 */ 
	if ( (bit < 1) || (bit > 24) ){ 
		data->stat = I8255_ST_BB; 
		return; 
		} 
 
	/*  Decrement the bit so we 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. 
	 *  Then form the bit mask, starting with 1 and 
	 *  left shifting to line it up with the proper bit. 
	 *  There will then be a set bit in the mask byte corresponding 
	 *  to the bit in the 8255 PORT to be toggled.  All other bits in 
	 *  the mask byte will be zero.  The current data is XORED with 
	 *  the mask and then output. 
	 */ 
	bit--; 
	port = ( bit / 8 );     /* port number (0 - 2)          */ 
	bit = bit % 8;          /* modulo to get the bit number */ 
	mask = 0x01;            /* assume low bit of byte       */ 
	mask = mask << bit;     /* shift left to requested bit  */ 
 
	/*  Switch to appropriate port and 
	 *  XOR port byte with mask byte. 
	 *  Obtain port address. 
	 */ 
	switch ( port ){ 
		case 0:         /* port A   */ 
			data->adat = data->adat ^ mask; 
			oval = data->adat; 
			padd = I8255_PORTA (data->base); 
			break; 
		case 1:         /* port B   */ 
			data->bdat = data->bdat ^ mask; 
			oval = data->bdat; 
			padd = I8255_PORTB (data->base); 
			break; 
		case 2:         /* port C   */ 
			data->cdat = data->cdat ^ mask; 
			oval = data->cdat; 
			padd = I8255_PORTC (data->base); 
			break; 
		default:        /* bad port number  */ 
			data->stat = I8255_ST_BP; 
			return; 
			break; 
		} 
 
	chp_portwt ( padd, oval ); 
	data->stat = I8255_ST_OK; 
	} 
 
/*- 
 *  ---------------------------------------------------------------------- 
 *  END I8255F09.C Source File 
 *  ---------------------------------------------------------------------- 
 */