C541U_99 Datasheet, PDF (82/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

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.
Buffer is empty:
USB write access enabled
CPU read access disabled
USB write
No
request?
Yes
Buffer is written by USB
EOD = 1
Buffer full?
No
Yes
Buffer is full:
USB write access disabled
CPU read access enabled
SOD = 1
Buffer can be read by CPU
Yes
Buffer empty?
No
MCD03400
Figure 6-20
USB Write Access in Single Buffer Mode - Buffer Handling
Semiconductor Group
6-37
1999-04-01