Figure 387. Otg A-B Device Connection; Otg Dual Role Device (Drd) - STMicroelectronics STM32F405 Reference Manual

RM0090
34.4

OTG dual role device (DRD)

1. External voltage regulator only needed when building a V
2. STMPS2141STR needed only if the application has to support a V
switch can be used if 5 V are available on the application board.
34.4.1 ID line detection
The host or peripheral (the default) role is assumed depending on the ID input pin. The ID
line status is determined on plugging in the USB, depending on which side of the USB cable
is connected to the micro-AB receptacle.
•
If the B-side of the USB cable is connected with a floating ID wire, the integrated pull-
up resistor detects a high ID level and the default Peripheral role is confirmed. In this
configuration the OTG_FS complies with the standard FSM described by section 6.8.2:
On-The-Go B-device of the On-The-Go Specification Rev1.3 supplement to the
USB2.0.
•
If the A-side of the USB cable is connected with a grounded ID, the OTG_FS issues an
ID line status change interrupt (CIDSCHG bit in OTG_FS_GINTSTS) for host software
initialization, and automatically switches to the host role. In this configuration the
OTG_FS complies with the standard FSM described by section 6.8.1: On-The-Go A-
device of the On-The-Go Specification Rev1.3 supplement to the USB2.0.
34.4.2 HNP dual role device
The HNP capable bit in the Global USB configuration register (HNPCAP bit in OTG_FS_
GUSBCFG) enables the OTG_FS core to dynamically change its role from A-host to A-
peripheral and vice-versa, or from B-Peripheral to B-host and vice-versa according to the
host negotiation protocol (HNP). The current device status can be read by the combined
values of the Connector ID Status bit in the Global OTG control and status register (CIDSTS
bit in OTG_FS_GOTGCTL) and the current mode of operation bit in the global interrupt and
status register (CMOD bit in OTG_FS_GINTSTS).
The HNP program model is described in detail in
model.

Figure 387. OTG A-B device connection

DocID018909 Rev 11
USB on-the-go full-speed (OTG_FS)
powered device
BUS
powered device. A basic power
BUS
Section 34.17: OTG_FS programming
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