SAM7X128_14 Datasheet, PDF (431/662 Pages) ATMEL Corporation – ARM-based Flash MCU

34.4 Typical Connection
Figure 34-2. Board Schematic to Interface USB Device Peripheral
5V Bus Monitoring
PIO
27 K
47 K
PIO
Pullup Control
0: Enable
1: Disable
DDM
DDP
R_EXT
R_EXT
330 K
3V3
1.5K
2
1
330 K
3 ^{Type B} 4
Connector
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 standard 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.
A termination serial resistor must be connected to DP and DM. The resistor value is defined in the electrical specification
of the product (R_EXT).
SAM7X Series [DATASHEET]
6120K–ATARM–11-Feb-14
431