Datasheet

SAM9G20
DS60001516A-page 660  2017 Microchip Technology Inc.
36.4.2 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 enable the integrated pulldown by disabling the transceiver (TXVDIS = 1) and then remove the pullup (PUON = 0).
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
).
36.5 Functional Description
36.5.1 USB V2.0 Full-speed Introduction
The USB V2.0 full-speed provides communication services between host and attached USB devices. Each device is offered with a collec-
tion of communication flows (pipes) associated with each endpoint. Software on the host communicates with a USB device through a set
of communication flows.
Figure 36-3: Example of USB V2.0 Full-speed Communication Control
The Control Transfer endpoint EP0 is always used when a USB device is first configured (USB v. 2.0 specifications).
EP0
USB Host V2.0
Software Client 1 Software Client 2
Data Flow: Bulk Out Transfer
Data Flow: Bulk In Transfer
Data Flow: Control Transfer
Data Flow: Control Transfer
EP1
EP2
USB Device 2.0
Block 1
USB Device 2.0
Block 2
EP5
EP4
EP0
Data Flow: Isochronous In Transfer
Data Flow: Isochronous Out Transfer
USB Device endpoint configuration requires that
in the first instance Control Transfer must be EP0.