SCD1284 INTEL [Intel Corporation], SCD1284 Datasheet - Page 111

• Manufacturer Part Number: SCD1284
• Description: IEEE 1284-Compatible Parallel Interface Controller with Two High-Speed Asynchronous Serial Ports
• Manufacturer: INTEL [Intel Corporation]

7.1.7
7.1.8
Datasheet
Register Name: PIR
Register Description: Parallel Interrupt
Access: Read/Write
Register Name: PPR
Register Description: Prescaler Period
Access: Read/Write
PPIreq
Bit 7
Bit 7
Bit
4:2
1:0
Bit
6:5
4:0
5
7
Parallel Interrupt Register
The PIR is a modified version of the other interrupt registers (RIR, TIR, and MIR) that
incorporates the unique differences between interrupt structures of the two major blocks of the
CD1284. The Ireq bit (bit 7) has the identical function as the Ireq bits in the TIR, RIR, and MIR.
Prescaler Period Register
The PPR sets the divisor that generates the time period for CD1284 timer operations. It can be set
to any value between 0 and 255 (x’FF). The PPR is clocked by the system clock prescaled
(divided) by 512.
Rxunfair, Txunfair, and Mdunfair: These bits are used by the internal processor to implement the Fair Share
service request function. If this bit is set, the CD1284 does not assert another service request of this type until
the bit is cleared by a pulse on the external SVCACK* pin. The unfair bits are forced to ‘0’, disabling the Fair
Share mechanism, by setting the Unfair bit in the PACR. These bits are not used in Poll mode.
These bits define the context of the current service-acknowledge cycle during Poll mode and are fixed by
hardware within the CD1284. These bits must be replicated exactly when the register is copied to the CAR
and is activating a service-acknowledge cycle. See the discussion of Poll-mode operation in
more detailed description.
ch[1:0]: These two bits encode the channel number of the requesting channel. During Poll-mode operation
when the RIR, TIR, and MIR are copied into the CAR to start the service routine, ch[1:0] set the channel
number that is serviced.
PPIreq: The internal processor sets this bit to generate the external service request output. It is a direct
reflection of the inverse state of the SVCREQP* pin; it is the active-high output of the latch that drives
SVCREQP*. This bit can be scanned by the host to detect an active service request. The bit is cleared by the
internal logic at the beginning of the hardware service-acknowledge cycle or by toggling the IntEn bit
(PFCR[4]).
PPort and Pipeline: These two bits indicate which of the two functional blocks of the parallel port are
requesting service. PPort set indicates that the parallel channel control state machine is the cause of the
request; Pipeline set indicates that the data pipeline is requesting service. Both bits set indicates that both
blocks are requesting service simultaneously.
Reserved: These bits always return ‘0’ when read by the host. Do not modify.
PPort
Bit 6
Bit 6
Pipeline
Bit 5
Bit 5
IEEE 1284-Compatible Parallel Interface Controller — CD1284
Bit 4
Bit 4
8-bit Binary Value
0
Description
Description
Bit 3
Bit 3
0
Bit 2
Bit 2
0
Bit 1
Bit 1
8-Bit Hex Address: 7E
8-Bit Hex Address: 61
0
Default Value: FF
Default Value: 00
Section 5.3
Bit 0
Bit 0
0
for a
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