參數(shù)資料
型號(hào): ISP1181
廠商: NXP Semiconductors N.V.
英文描述: Full-speed Universal Serial Bus Interface Device(全速通用串行總線接口器件)
中文描述: 全速通用串行總線接口設(shè)備(全速通用串行總線接口器件)
文件頁數(shù): 15/69頁
文件大小: 1655K
代理商: ISP1181
Philips Semiconductors
ISP1181
Full-speed USB interface
Objective specification
Rev. 01 — 13 March 2000
15 of 69
9397 750 06896
Philips Electronics N.V. 2000. All rights reserved.
The following example shows the steps which occur in a typical DMA transfer:
1. ISP1181 receives a data packet in one of its endpoint FIFOs; the packet must be
transferred to memory address 1234H.
2. ISP1181 asserts the DREQ signal requesting the 8237 for a DMA transfer.
3. The 8237 asks the CPU to release the bus by asserting the HRQ signal.
4. After completing the current instruction cycle, the CPU places the bus control
signals (MEMR, MEMW, IOR and IOW) and the address lines in three-state and
asserts HLDA to inform the 8237 that it has control of the bus.
5. The 8237 now sets its address lines to 1234H and activates the MEMW and IOR
control signals.
6. The 8237 asserts DACK to inform the ISP1181 that it will start a DMA transfer.
7. The ISP1181 now places the byte or word to be transferred on the data bus lines,
because its RD signal was asserted by the 8237.
8. The 8237 waits one DMA clock period and then de-asserts MEMW and IOR. This
latches and stores the byte or word at the desired memory location. It also
informs the ISP1181 that the data on the bus lines has been transferred.
9. The ISP1181 de-asserts the DREQ signal to indicate to the 8237 that DMA is no
longer needed. In
Single cycle mode
this is done after each byte or word, in
Burst mode
following the last transferred byte or word of the DMA cycle.
10. The 8237 de-asserts the DACK output indicating that the ISP1181 must stop
placing data on the bus.
11. The 8237 places the bus control signals (MEMR, MEMW, IOR and IOW) and the
address lines in three-state and de-asserts the HRQ signal, informing the CPU
that it has released the bus.
12. The CPU acknowledges control of the bus by de-asserting HLDA. After activating
the bus control lines (MEMR, MEMW, IOR and IOW) and the address lines, the
CPU resumes the execution of instructions.
For a typical bulk transfer the above process is repeated 64 times, once for each byte.
After each byte the address register in the DMA controller is incremented and the
byte counter is decremented. When using 16-bit DMA the number of transfers is 32
and address incrementing and byte counter decrementing is done by 2 for each word.
10.3 DACK-only mode
The DACK-only DMA mode is selected by setting bit DAKOLY in the Hardware
Configuration Register (see
Table 22
). The pin functions for this mode are shown in
Table 9
. A typical example of ISP1181 in DACK-only DMA mode is given in
Figure 4
.
Table 9:
Symbol
DREQ
DACK
DACK-only mode: pin functions
Description
DMA request
DMA acknowledge
I/O
O
I
Function
ISP1181 requests a DMA transfer
DMA controller confirms the transfer;
also functions as data strobe
DMA controller terminates the transfer
not used
not used
EOT
RD
WR
End-Of-Transfer
read strobe
write strobe
I
I
I
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