C541U_99 Datasheet, PDF (114/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

On-Chip Peripheral Components
C541U
Bit
SETWRn
CLREPn
DONEn
Function
Set direction of USB memory buffer to write
Bit SETWRn is used to predict the direction of the next USB access for endpoint
n as an USB write access. A faulty prediction causes no errors since the USB
module determines the real direction. A change in the data direction is only
executed, if both USB memory buffers are empty. SETWR cannot be set together
with CLREPn because a change of bit DIRn during a transfer is not allowed.
Note : bits SETWRn and SETRDn must not be set at a time.
Clear endpoint
Setting bit CLREPn will set the address offset register for a CPU access to USB
memory to 0. The bits CBFn and UBFn will be reset when CLREPn is set.
Bit CLREPn is reset by hardware. A read operation on this bit will always deliver
0. Setting of CLREPn does not change the direction of endpoint n. This means, bit
DIRn is not changed.
Note: When bits CLREPn and ESPn are set simultaneously with one instruction,
bit ESPn remains set and the next status phase is enabled. If only CLREPn
is set, bit ESPn is reset and the status phase is disabled.
Setting bits CLREPn and SETRDn or SETWRn simultaneously with one
instruction is not allowed. This means that the information of SETRDn or
SETWRn is ignored in this case.
Buffer done by CPU
If bit DONE is set, the current USB memory buffer assigned to CPU is
automatically tagged full (data flow from the CPU to the USB) or empty (data flow
from the USB to the CPU). This bit is reset by hardware after it has been set. A
read operation on this bit will deliver always 0.
Note: If the direction of endpoint n is read (USB read access) and auto-increment
is enabled (INCEn=1) and DONEn is set the content of register ADROFF
is copied automatically to register EPLENn of the actual endpoint. Register
EPLENn is not changed if the auto-increment capability is disabled
(INCEn=0).
Semiconductor Group
6-69
1999-04-01