SCD1284 datasheet(95/176 Pages) INTEL

95 / 176 page

IEEE 1284-Compatible Parallel Interface Controller — CD1284

Datasheet

switch (status) {

case 1:

/* all values that include a receive

request */

case 3:

case 5:

case 7:

case 0xF:

rx_stat = service_rec( );

return(rx_stat);

break;

case 2:

/* all values that include transmit but

not receive */

case 6:

case 0xA:

case 0xE:

tx_stat = service_txm( );

return(tx_stat);

break;

case 4:

/* modem service request */

case 0xC:

md_stat = service_mdm( );

return(md_stat);

break;

case: 8:

/* parallel port service request */

par_stat = service_par();

return(par_stat);

break;

default:

/* can’t happen */

break;

}

Once the code above locates an active request posted in the SVRR, it calls the appropriate

subroutine to service the request. The service routines follow.

6.3.1.2

Serial Receive Service

/* The receive service acknowledge cycle begins by reading the RIR. This register

contains the necessary information to switch the CD1284 into the correct service

acknowledge context. The RIR is saved for use at the end of the routine and then

copied into the CAR. The act of copying the RIR into the CAR forces the context

switch. The channel number requesting service is extracted from the RIR. The RIVR

used to correctly handle the request. At the end of the service, the upper two bits

in the RIR are cleared causing the switch out of the service acknowledge context. */

service_rec( )

{

char

serv_type, save_rir, save_car, channel, status, char;

int

char_count, i;

save_rir = inportb(RIR);

/* retrieve and save receive interrupt

value */

channel = save_rir & 0x03;

/* extract channel number from the RIR*/

save_car = inportb(CAR);

/* save CAR for restore */

outportb(CAR, save_rir);

/* switch CD1284 to service ack. context

serv_type = inportb(RIVR) & 0x07; /* read vector register; get type (good/

exception)*/

switch (serv_type) {

case 3:

/* good data service */

char_count = inportb(RDCR);

/* get number of

characters in FIFO */

for ( i = 1; i <= char_count; i++) {/* - read that number of

chars */

char = inportb(RDSR);

/* read char from FIFO */

SCD1284 Datasheet(PDF) 95 Page - Intel Corporation

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