參數(shù)資料
型號: AM79C974KCW
廠商: ADVANCED MICRO DEVICES INC
元件分類: 微控制器/微處理器
英文描述: PCnetTM-SCSI Combination Ethernet and SCSI Controller for PCI Systems
中文描述: 2 CHANNEL(S), 10M bps, LOCAL AREA NETWORK CONTROLLER, PQFP132
封裝: PLASTIC, QFP-132
文件頁數(shù): 79/153頁
文件大小: 838K
代理商: AM79C974KCW
P R E L I M I N A R Y
AMD
79
Am79C974
18681A/1-31
0
31
0
31
SMDLA
WMAC
0
12
31
Page Frame Address #1
Page Frame Address #2
Page Frame Address #3
Page Frame Address #4
MDL
Ignored
Page Frame Address #n
Ignored
Ignored
Ignored
Ignored
In this example, the contents of the WMAC register is
pointing to page frame address #1. When the first entry
in the MDL is read (page frame address #1), the WMAC
register is incremented to point to the next page entry
(page frame address #2).
2. Issue the Start DMA Command.
The SCSI control-
ler reads the page frame address (bits 31:12) from
the MDL entry and combines it with the first page
offset value in the Starting Physical Address (SPA)
register (bits 11:0). This 32-bit value is loaded into
the Working Address Counter (WAC) register and
becomes the physical address for page#1, as
shown below. The WMAC is then incremented to
point to the next entry in the MDL.
0
12
31
WAC
4K Page #1
Page Frame Address #1
Starting Offset
From the MDL
0
12
31
SPA
XXXX
Starting Offset
Programmed by
the software
Data
18681A/1-32
3. When the WAC register (bits 11:0) reaches the
first 4K byte boundary, the SCSI controller reads
the second MDL entry and combines the page
frame address (bits 31:12) from this entry of the
MDL with bits 11:00 of the WAC register. This be-
comes the physical address for page#2. Since the
WAC register (bits 11:0) has rolled over to ‘00h’,
the WAC now points to the beginning of the Page
Frame Address #2 as shown below. The WMAC
is then incremented to point to the next entry in
the MDL.
18681A/1-33
0
12
31
WAC
4K Page #2
0
Page Frame Address #2
From the MDL
Data
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