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參數(shù)資料
| 型號： | NS32490D |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | NIC Network Interface Controller(NIC網(wǎng)絡(luò)接口控制器) |
| 中文描述： | NIC網(wǎng)絡(luò)接口控制器（NIC網(wǎng)絡(luò)接口控制器） |
| 文件頁數(shù)： | 36/56頁 |
| 文件大?。?/td> | 689K |
| 代理商： | NS32490D |
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13.0 Bus Arbitration and Timing
(Continued)
REMOTE READ TIMING
1) The DMA reads byte/word from local buffer memory and
writes byte/word into latch, increments the DMA address
and decrements the byte count (RBCR0,1).
2) A Request Line (PRQ) is asserted to inform the system
that a byte is available.
3) The system reads the port, the read strobe (RACK) is
used as an acknowledge by the Remote DMA and it goes
back to step 1.
Steps 1–3 are repeated until the remote DMA is com-
plete.
Note that in order for the Remote DMA to transfer a byte
from memory to the latch, it must arbitrate access to the
local bus via a BREQ, BACK handshake. After each byte or
word is transferred to the latch, BREQ is dropped. If a Local
DMA is in progress, the Remote DMA is held off until the
local DMA is complete.
TL/F/8582–72
REMOTE WRITE TIMING
A Remote Write operation transfers data from the I/O port
to the local buffer RAM. The NIC initiates a transfer by re-
questing a byte/word via the PRQ. The system transfers a
byte/word to the latch via IOW, this write strobe is detected
by the NIC and PRQ is removed. By removing the PRQ, the
Remote DMA holds off further transfers into the latch until
the current byte/word has been transferred from the latch,
PRQ is reasserted and the next transfer can begin.
1) NIC asserts PRQ. System writes byte/word into latch.
NIC removes PRQ.
2) Remote
byte/word to local buffer memory, increments address
and decrements byte count (RBCR0,1).
DMA
reads
contents
of
port
and
writes
3) Go back to step 1.
Steps 1–3 are repeated until the remote DMA is com-
plete.
TL/F/8582–73
36
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