C541U_99 Datasheet, PDF (102/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

On-Chip Peripheral Components
C541U
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 D4H)
Reset Value : 00H
Bit No. MSB
LSB
7
6
5
4
3
2
1
0
D4H
0
0
AO5 AO4 AO3 AO2 AO1 AO0 ADROFF
r
r
rw
rw
rw
rw
rw
rw
Bit
AO5-0
0
Function
USB address offset register
AO5-0 stores the 6-bit offset address for USB memory buffer addressing by the
CPU.
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
6-57
1999-04-01