C541U_99 Datasheet, PDF (104/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

On-Chip Peripheral Components
C541U
6.4.7.2 Device Registers
The device registers can only be accessed when global register EPSEL(D2H) = 80H. The following
SFRs are defined as device register :
– DCR Device Control Register
– DPWDR Device Power Down Register
– DIER Device Interrupt Enable Register
– DIRR Device Interrupt Request Register
– FNRL Frame Number Register (low byte)
– FNRH Frame Number Register (high byte)
The device control register includes control and status bits which indicate the current status of the
USB module and the status of the USB bus.
USB Device Control Register DCR (Address C1H)
Bit No. MSB
7
6
C1H SPEED DA
rw
r
5
SWR
rw
4
SUSP
r
3
DINIT
r
2
RSM
rw
Reset Value : 000X0000B
LSB
1
0
UCLK PCLK DCR
rw
rw
Bit
SPEED
DA
SWR
SUSP
Function
Low / full speed select
Bit SPEED configures the USB module in the C541U for full speed (12 MBaud) or
low speed (1.5 MBaud) mode. This bit can only be written with bit SWR=1
(software reset). After hardware reset the USB module runs in low speed mode
and the PLLx4 is automatically disabled.
If SPEED=0, low speed mode selected (default after reset)
If SPEED=1, full speed mode selected.
Device attached
Bit DA reflects the state of pin DADD, which can be used to indicate whether the
device is attached to the USB bus or not in self-powered mode.
If pin DADD is 0, bit DA=0.
If pin DADD is 1, bit DA=1.
Software reset
Setting bit SWR initiates a software reset operation of the USB device. This bit is
cleared by hardware after successful reset operation. SWR can not be reset by
software.
Suspend mode
This bit is set when the USB is idle for more than 3 ms. It will remain set until there
is a non idle state on the USB cable or when bit RSM is set.
Semiconductor Group
6-59
1999-04-01