SCD1284 datasheet(94/176 Pages) INTEL

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CD1284 — IEEE 1284-Compatible Parallel Interface Controller

Datasheet

outportb(CAR, chan);

/* set channel number in CAR */

outportb(RTPR, 0x14);

/* set channel time-out value (20ms) */

outportb(TCOR, 0x01);

/* constants for 25 MHz clock – clock option*/

outportb(TBPR, 0x51);

– baud rate period */

outportb(RCOR, 0x01);

/* constants for 25 MHz clock – clock option*/

outportb(RBPR, 0x51);

– baud rate period */

outportb(COR1, 0x03);

/* no parity, 1 stop bit, 8 bit chars */

outportb(COR2, 0x40);

/* auto. in-band flow control */

outportb(COR3, 0x38);

/* transp. flow-control, special char 1 & 2 detect,

fifo thresh = 8 */

while (inportb(CCR) != 0)/* make sure that CCR is zero before issuing

commands */

;

outportb(CCR, 0x4E);

/* issue COR changed command for COR1, 2, 3 */

outportb(COR5, 0x80);

/* enable ISTRIP */

outportb(SRER, 0x14);

/* enable receive and transmit interrupts */

while (inportb(CCR) != 0)/* make sure that CCR is zero before issuing

commands */

;

outportb(CCR, 0x1A);

/* issue receiver and transmitter enable command to

CCR */

}

6.3

Serial Poll Mode Examples

The CD1284 provides a set of seven registers dedicated to Poll-mode operation, described in

Chapter 5.0. This section shows one of many ways that these registers are used to detect and

service requests from any of the channels receiver, transmitter, or modem signal change functions.

The primary registers involved in polling are: SVRR, RIR, TIR, MIR, and CAR. The

supplementary registers are: RIVR, TIVR, and MIVR. Of the latter three registers, only RIVR is

actually used. RIVR provides the service request status for ‘good’ data or exception data. The

TIVR and MIVR provide redundant information and are rarely used. Other registers related to

service requests (TDR, RDSR, MISR, and so on) perform the same functions as in hardware-

acknowledged service requests. The parallel channel uses a slightly different register manipulation

procedure and is shown separately. The top-level polling routine is the same regardless of the type

of request serviced.

Once again, C code fragments describe the functions. As with other coding examples, it is assumed

that register addresses are defined elsewhere, such as in a header file. The routines cannot be

considered complete. The routines cannot be considered complete; some pieces are dependent on

the system software design and the code presented is only an example. The pieces do, however,

show methods used to implement the poll mode service request/service acknowledge sequence.

6.3.1

Polling Routine Examples

6.3.1.1

Scanning Loop

/* Poll-mode code fragments routinely check for any servicing requests and branches

to the appropriate service routine. The code prioritizes service requests as receive,

transmit, modem and parallel, in that order. System design dictates the actual

priorities required. Note that the routine ignores the state of the DMA active bit.

poll( )

{

char

status;

char

rx_stat = tx_stat = md_stat = 0, par_stat = 0;

if (status = inportb(SVRR) & 0x0F) {/* Mask off DMA status */

SCD1284 Datasheet(PDF) 94 Page - Intel Corporation

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