PIC32MX440F256H-80I Datasheet, PDF (281/646 Pages) Microchip Technology – 64/100-Pin General Purpose and USB 32-Bit Flash Microcontrollers

• Optionally supports Session Request Protocol
(SRP)
• Can be bus-powered or self-powered
11.4.3 OTG DUAL ROLE
The OTG dual role device supports both USB host and
device functionality. OTG dual role devices use a
micro-AB receptacle. This allows a micro-A or a micro-
B plug to be attached. Both the micro-A and micro-B
plugs have an additional pin, the ID pin, to signify which
plug type was connected. The plug type connected to
the receptacle, micro-A or micro-B, determines the
default role of the OTG device, host or device. An OTG
device will perform the role of a host when a micro-A
plug is detected. When a micro-B plug is detected, the
role of a USB device is performed.
When an OTG device is directly connected to another
OTG device using an OTG cable (micro-A to micro-B),
Host Negotiation Protocol (HNP) can be used to swap
the roles of host and USB device between the two with-
out disconnecting and reconnecting the cable. To differ-
entiate between the two OTG devices, the term “A-
device” refers to the device connected to the micro-A
plug and “B-device” refers to the device connected to
the micro-B plug.
11.4.3.1 A-Device, the Default Host
In OTG dual role, operating as a host, the following fea-
tures and requirements describe an A-device:
• Supports the devices on the TPL (class support is
not allowed)
• Required to support those transaction types that
are required by devices in the TPL
• USB hub support is optional
• Device drivers are not required to be updateable
• A single micro-AB receptacle is used
• Full-speed protocol must be supported (high-
speed and/or low-speed protocol can be
supported)
• USB port must be able to deliver a minimum of 8
mA for a configured or unconfigured device, and
optionally, up to 500 mA for a configured device
• Supports HNP; the host can switch roles to
become a device
• Supports at least one form of SRP
• A-device supplies VBUS power when the bus is
powered, even if the roles are swapped using
HNP
11.4.3.2 B-Device, the Default Device
In OTG dual role, operating as a USB device, the fol-
lowing features and requirements describe a B-Device:
• Class- or vendor-specific functionality
• Draws 8 mA or less before configuration
• Is typically self-powered, due to low-current
PIC32MX3XX/4XX
requirements, but can draw up to 500 mA after
successful negotiation with the host
• A single micro-AB receptacle is used
• Must support full-speed protocol (support of low-
speed and/or high-speed protocol is optional
• Supports control transfers, and supports data
transfers as they are required for implementation
• Supports both forms of SRP – VBUS pulsing and
data-line pulsing
• Supports HNP
B-device does not supply VBUS power, even if the roles
are swapped using HNP.
Note:
Dual role devices that do not support full
OTG functionality are possible using mul-
tiple USB receptacles. However, there
may be special requirements if those
devices are to be made USB compliant.
Refer to the USB implementer’s forum for
the most current details.
•
11.4.4 PHYSICAL BUS INTERFACE
11.4.4.1 Bus Speed Selection
The USB specification defines full-speed operation as
12 Mb/s and low speed operation as 1.5 Mb/s. A data
line pull-up resistor is used to identify a device as full
speed or low speed. For full-speed operation, the D+
line is pulled up; for low-speed operation, the D- line is
pulled up.
11.4.4.2 VBUS Control
VBUS is the 5V USB power supplied by the host or a
hub to operate bus-powered devices. The need for
VBUS control depends on the role of the application. If
VBUS power must be enabled and disabled, the control
must be managed by firmware.
The following list details the VBUS requirements:
• Standard host typically supplies power to the bus
at all times.
• Host may switch off VBUS to conserve power
• USB device never powers the bus – VBUS pulsing
may be supported as part of the SRP.
• OTG A-device supplies power to the bus, and
typically turns off VBUS to conserve power.
• OTG B-device can pulse VBUS for SRP.
Note: Refer to the specific device data sheet for
VBUS electrical parameters.
© 2008 Microchip Technology Inc.
Preliminary
DS61143E-page 279