C541U_99 Datasheet, PDF (132/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

On-Chip Peripheral Components
C541U
6.4.11 Detach / Attach Detection
The USB device can be used in two different modes concerning its power supply, the bus-powered
mode and the self-powered mode.
6.4.11.1 Self-Powered Mode
In self-powered mode, the USB device has its own power supply. The USB device has to detect
whether it is connected to USB bus or not. This detection is done by hardware by using the Device-
Attached Device-Detached pin DADD. When the device-attached condition is detected, bit DA in
the device control register DCR is set and a device interrupt can be generated if required (bit DAI in
SFR DIRR is set). The interrupt service routine of this device interrupt must completely initialize the
USB device/module. The device-detached detection resets bit DA (and sets bit DDI in SFR DIRR)
and can generate a device interrupt, too.
6.4.11.2 Bus-Powered Mode
In bus-powered mode, the USB device is driven by the power supply from the USB bus. The
maximum power consumption is given by the USB specification. In order to respect this
specification, the power consumption in suspend mode should not exceed 500 µA.
An explicit device-attached detection in this mode is not necessary. If the CPU is running, the device
is attached, so the USB device/module has to be configured only after power-on. The device-detach
action has no significance concerning software, because the device is no longer powered and the
CPU stops. As a result, no attach-detach detection is needed. In this mode, pin DADD can be used
as standard IO pin with bit DA monitoring its status and the interrupt generation on DA should not
be used. If the interrupt generation on bit DA remains activated, a request must not be interpreted
as attached-detached action, but as an external interrupt request on pin DADD, which is generating
a device interrupt.
Semiconductor Group
6-87
1999-04-01