Datasheet

438
6120F–ATARM–03-Oct-06
AT91SAM7X512/256/128 Preliminary
34.4 Typical Connection
Figure 34-2. Board Schematic to Interface USB Device Peripheral
34.4.1 USB Device Transceiver
The USB device transceiver is embedded in the product. A few discrete components are
required as follows:
• the application detects all device states as defined in chapter 9 of the USB specification;
– pullup enable/disable
–VBUS monitoring
• to reduce power consumption the host is disconnected
• for line termination.
Pullup enable/disable is done through a MOSFET controlled by a PIO. The pullup is enabled
when the PIO drives a 0. Thus PIO default state to 1 corresponds to a pullup disable. Once the
pullup is enabled, the host will force a device reset 100 ms later. Bus powered devices must
connect the pullup within 100 ms.
34.4.2 VBUS Monitoring
VBUS monitoring is required to detect host connection. VBUS monitoring is done using a stan-
dard PIO with internal pullup disabled. When the host is switched off, it should be considered as
a disconnect, the pullup must be disabled in order to prevent powering the host through the pull-
up resistor.
When the host is disconnected and the transceiver is enabled, then DDP and DDM are floating.
This may lead to over consumption. A solution is to connect 330 KΩ pulldowns on DP and DM.
These pulldowns do not alter DDP and DDM signal integrity.
3V3
R
EXT
DDM
DDP
PIO
PIO
27 K
47 K
330 K
Type B
Connector
12
34
5V Bus Monitoring
Pullup Control
R
EXT
330 K
1.5K
0: Enable
1: Disable