Semiconductor Group
6-37
1999-04-01
On-Chip Peripheral Components
C541U
6.4.2.2
Single Buffer Mode
In single buffer mode the USB and the CPU share one common USB memory page. The active
buffer page can be either page 0 or page 1. Back-to-back transfers are not possible in this mode.
Easy data storage and controlling can be achieved in this mode. E.g. a once created data set for an
interrupt endpoint can be stored permanently in USB memory. As a result, an additional memory
space for data storage is no longer needed.
6.4.2.2.1 USB Write Access
Figure 6-20 shows the basic flowchart of a USB write access to one USB memory buffer in single
buffer mode.
Figure 6-20
USB Write Access in Single Buffer Mode - Buffer Handling
Buffer is empty:
USB write access enabled
CPU read access disabled
No
CPU read access enabled
USB write access disabled
Buffer is full:
SOD = 1
Buffer full?
Buffer is written by USB
No
EOD = 1
MCD03400
Yes
Yes
Yes
USB write
request?
No
Buffer empty?
Buffer can be read by CPU
Содержание C541U
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