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EBIU Overview
6-8
ADSP-BF537 Blackfin Processor Hardware Reference
Bus Request and Grant
The processor can relinquish control of the data and address buses to an
external device. The processor three-states its memory interface to allow
an external controller to access either external asynchronous or synchro-
nous memory parts.
Operation
When the external device requires access to the bus, it asserts the bus
request (
BR
) signal. The
BR
signal is arbitrated with EAB requests. If no
internal request is pending, the external bus request will be granted. The
processor initiates a bus grant by:
• Three-stating the data and address buses and the asynchronous
memory control signals. The synchronous memory control signals
can optionally be three-stated.
• Asserting the bus grant (
BG
) signal.
The processor may halt program execution if the bus is granted to an
external device and an instruction fetch or data read/write request is made
to external memory. When the external device releases
BR
, the processor
deasserts
BG
and continues execution from the point at which it stopped.
The processor asserts the
BGH
pin when it is ready to start another external
port access, but is held off because the bus was previously granted.
When the bus has been granted, the
BGSTAT
bit in the
SDSTAT
register is
set. This bit can be used by the processor to check the bus status to avoid
initiating a transaction that would be delayed by the external bus grant.
a
If the system is using SDRAM, be sure to place the SDRAM into
self-refresh mode before busmastership is granted. If this is not
done, the SDRAM’s data is lost.
Содержание Blackfin ADSP-BF537
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Страница 90: ...Development Tools 1 32 ADSP BF537 Blackfin Processor Hardware Reference ...
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Страница 340: ...SDC Programming Examples 6 84 ADSP BF537 Blackfin Processor Hardware Reference ...
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Страница 720: ...Electrical Specifications 11 60 ADSP BF537 Blackfin Processor Hardware Reference ...
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Страница 1162: ...G 26 ADSP BF537 Blackfin Processor Hardware Reference ...
Страница 1218: ...Index I 56 ADSP BF537 Blackfin Processor Hardware Reference ...