Siemens C541U User Manual page 102

In most cases the CPU accesses only one endpoint buffer until it is full (CBF=1 at CPU write access)
or empty (CBF=0 at CPU read access). As the USB memory size is 128 bytes per page, the
maximum packet length is limited to 64 bytes. Therefore, only the lowest 6 bits of ADROFF
(AO5..AO0) are required for offset definiton.
A write operation to ADROFF is only successful if either DIR=0 and CBF=1 (write operation) or
DIR=1 and CBF=0 (read operation).
USB Address Offset Register ADROFF (Address D4 H )
Bit No. MSB
7
D4 H
0
r
Bit Function
AO5-0 USB address offset register
AO5-0 stores the 6-bit offset address for USB memory buffer addressing by the
CPU.
0 Reserved for future use. For compatiblity, these bits have to be ignored in all read
accesses and written with zero in all write accesses.
After each modification (automatical or by write action) of the address offset register ADROFF, the
value pointed to is automatically read out of USB memory and transferred to register USBVAL.
Semiconductor Group
6 5 4
0 AO5 AO4
r rw rw
On-Chip Peripheral Components
3 2
AO3 AO2
rw rw
6-57
Reset Value : 00 H
LSB
1 0
AO1 AO0 ADROFF
rw rw
1999-04-01
C541U