CD1284 datasheet(97/176 Pages) INTEL

97 / 176 page

IEEE 1284-Compatible Parallel Interface Controller — CD1284

Datasheet

least-significant two bits; the main driver software must perform the necessary

functions. As with the receive and transmit routines, the Interrupt register, this

time the MIR, is used to force the CD1284 into the service context. */

service_mdm( )

{

char

save_mir, channel, save_car, mdm_status;

save_mir = inportb(MIR);

/* retrieve and save modem interrupt value

channel = save_mir & 0x03;

/* extract channel number from the MIR*/

save_car = inportb(CAR);

/* save CAR for restore */

outportb(CAR, save_mir);

/* switch CD1284 to service ack. context

mdm_status = inportb(MISR);

/* get status of which modem signals

changed */

outportb(MIR, save_mir & 0x3f)

/* terminate the service ack. sequence */

outportb(CAR, save_car);

/* restore CAR */

return(mdm_status | channel);

}

6.4

Hardware-Activated Service Examples

In nearly all respects, the way that the CPU interacts with the CD1284 during hardware-activated

service acknowledge is the same as software-activated methods. The main difference is that the

SVCACK* input signals perform the context switch automatically, relieving that duty from the

CPU. The result is the same: the CAR is set to point to the correct channel and the device is placed

in the proper internal mode to service the request.

When the SVCACK* input is activated, a read cycle is performed. The CD1284 places the contents

of the appropriate Interrupt Vector register (RIVR, TIVR, MIVR) of the channel requesting service

on the data bus. The CPU uses the information provided to determine the type of service and the ID

number of the device being accessed in the case of daisy-chained multiple CD1284s.

At the end of the service routine, the CPU writes a dummy value to the EOSRR. This causes the

switch out of the service acknowledge context and restores the environment to what it was before

the service began. Again, the parallel port service is slightly different and it is shown separately.

The following code fragments show the differences between this type of service acknowledge and

the types shown above for the software-activated context switch. Only the beginning and ending

steps are shown; the code between is very similar to the previous examples. These routines can be

executed as the result of a hardware interrupt or by software polling as in the previous examples.

For the purpose of this discussion, the method of arriving at the proper service routine is not

important.

6.4.1

Serial Receive Service

/* The receive service acknowledge cycle begins by executing a service acknowledge

cycle, which activates the SVCACKR* input. The data obtained as a result of this

‘read’ cycle is the contents of the RIVR register of the channel making the service

request. The service routine decodes the vector in the least significant three bits

to determine if the data is ‘good’ or ‘bad’ (exception). The context switch is done

automatically when the SVCACKR* signal is activated and the CAR does not need to be

loaded. The routine reads the RICR to determine the requesting channel number. If

this is a multiple–CD1284 system using daisy-chaining, the routine extracts the chip

ID from the upper five bits of the RIVR. */

service_rec( )

{

CD1284 Datasheet(PDF) 97 Page - Intel Corporation

CD1284 Datasheet(HTML) 97 Page - Intel Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL