參數(shù)資料
型號(hào)： CD1283
廠商： Intel Corp.
英文描述： IEEE 1284-Compatible Parallel Interface
中文描述： 符合IEEE 1284兼容并行接口
文件頁(yè)數(shù)： 55/94頁(yè)
文件大?。?/td> 1237K
代理商： CD1283
IEEE 1284-Compatible Parallel Interface
—
CD1283
Datasheet
55
7.1.6
Prescaler Period Register
The PPR sets the divisor used to generate the time period for CD1283 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. For best device operation, the value loaded into the PPR should not be less than
x
’
30.
7.1.7
Service Request Register
The SVRR reflects the inverse of the state of the service request pins (DMAREQ* and
SVCREQP*). Its primary use is in polled systems, and it allows system software to determine
what, if any, service requests are pending
.
Bit
Description
7
PPireq:
Internal logic 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 the SVCREQP*
pin. This bit can be scanned by the host to detect an active service request. This bit is cleared by the internal
logic at the beginning of the hardware service-acknowledge cycle or by toggling InTen (PFCR[4]). Clearing
PIR automatically deactivates the SVCREQP* output and clears the SRP bit (SVRR[3]).
6:5
PPort and Pipeline:
These two bits indicate which of the two functional blocks of the parallel port are
requesting service. When PPort is set, it indicates that the parallel channel control state machine is the
cause of the request; when Pipeline is set, it indicates that the data pipeline is requesting service. If both bits
are set, it indicates that both blocks are requesting service simultaneously.
4:0
Reserved:
The remainder of the bits in the PIR always return
‘
0
’
when read by the host and should not be
modified.
Register Name: PPR
Register Description: Prescale Period
Access: R/W
8-Bit Hex Address: 7E
Default Value: FF
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Binary Value
Register Name: SVRR
Register Description: Service Request
Access: Read only
8-Bit Hex Address: 67
Default Value: 00
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
DMAREQ
X
X
X
SRP
X
X
X
Bit
Description
7
DMA Request Status:
When this bit is set to
‘
1
’
, it indicates that a request is pending.
6:4
These bits are not used and are don
’
t cares.
3
Service Request Parallel:
When this bit is set to
‘
1
’
, it indicates that a request is pending.
2:0
These bits are not used and are don
’
t cares.
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