Semiconductor Group
6-41
1999-04-01
On-Chip Peripheral Components
C541U
The start-of-frame-done enable feature (SOFDE=1) is useful for USB memory read accesses when
the number of data bytes to be transferred from CPU to USB is not predictable (see figure 6-24).
The CPU can write data as desired to USB memory until a SOF occures (every 1 ms). The
automatic setting of bit SOF causes bit EOD to be set (at
). This indicates the CPU that no CPU
action on this buffer is required until a USB read operation has been finished (bit SOD set at
).
Setting of SOD indicates an empty USB memory to the CPU which can start again writing data into
USB memory.
Figure 6-24
Single Buffer Mode : USB Read Access with Start-of-Frame-Done Enabled
1
2
1
SOD
set
2
Frame n
Frame n+1
SOD
set
Time
SOF (n)
and EOD
set
and EOD
SOF (n+1)
set
Number of
Data Bytes
in USB Buffer
MaxLen
USB read accesses
CPU write accesses
MCT03404
Содержание C541U
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