參數(shù)資料
型號(hào): AM79C974
廠商: Advanced Micro Devices, Inc.
英文描述: PCnetTM-SCSI Combination Ethernet and SCSI Controller for PCI Systems
中文描述: PCnetTM -的SCSI結(jié)合以太網(wǎng)和SCSI控制器PCI系統(tǒng)
文件頁數(shù): 144/153頁
文件大小: 838K
代理商: AM79C974
AMD
A M E N D M E N T
10
Am79C974
Bus Master DMA Transfers
There are four primary types of DMA transfers. The
Am79C974 controller uses non-burst as well as burst
cycles for read and write access to the main memory.
Basic Non-Burst Read Cycles
All Am79C974 controller non-burst read accesses are of
the PCI command type Memory Read (type 6). Note that
during all non-burst read operations, the Am79C974
controller will always activate all byte enables, even
though some byte lanes may not contain valid data as
indicated by a buffer pointer value. In such instances,
the Am79C974 controller will internally discard un-
needed bytes.
Figure 6 shows a typical non-burst read access. The
Am79C974 controller asserts
IRDY
at clock 5 immedi-
ately after the address phase and starts sampling
DEVSEL
. The target extends the cycle by asserting
DEVSEL
not until clock 6. Additionally, the target inserts
one wait state by asserting its ready (
TRDY
) at clock 8.
18681A/1-10
FRAME
CLK
AD
IRDY
TRDY
C/
BE
DEVSEL
REQ
GNT
1
2
3
4
5
6
7
8
0000
9
PAR
PAR
PAR
DATA
DEVSEL
is sampled by the Am79C974 controller.
ADDR
0110
Figure 6. Non-Burst Read Cycles With Wait States
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