Semiconductor Group
6-59
1999-04-01
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)
Reset Value : 000X0000B
Bit
Function
SPEED
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.
DA
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.
SWR
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.
SUSP
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.
MSB
LSB
DCR
SPEED
DA
SWR
SUSP
DINIT
RSM
UCLK
PCLK
7
6
5
4
3
2
1
0
Bit No.
rw
r
rw
r
r
rw
rw
rw
C1H
Содержание C541U
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