Semiconductor Group
6-42
1999-04-01
On-Chip Peripheral Components
C541U
6.4.2.3
Dual Buffer Mode
In dual buffer mode, both USB memory pages (page 0 and page 1) are used for data transfers. The
logical assignment of the memory pages to CPU or USB is automatically switched. The following
two figures show the buffer handling concept in dual buffer mode for the USB read access and USB
write access.
Figure 6-25
USB Read Access in Dual Buffer Mode - Buffer Handling
CPU Buffer Handling
CPU page is empty : CBF = 0
CPU write access enabled
CPU writes 1 Byte
CPU buffer
full?
CPU buffer is full : CBF = 1
CPU write access disabled
Pages are (CBF = 1 and UBF = 0)
EOD = 1
USB page
empty?
SOD = 1
Yes
Yes
No
No
No
Yes
Yes
full?
CPU page
USB read access disabled
USB buffer is empty: UBF = 0
request?
USB read
USB reads buffer
USB read access enabled
USB page is full : UBF = 1
USB Buffer Handling
No
MCB03405
swapped
Содержание C541U
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