Otg Dual Role Device (Drd); Id Line Detection; Figure 396. Otg_Fs A-B Device Connection - ST STM32F423 Reference Manual

RM0430
protocol (SRP), detect valid startup and end-of-session conditions, and constantly
monitor the V
•
V
BUS
the SRP (weak drive).
Caution: To guarantee a correct operation for the USB OTG FS peripheral, the AHB frequency should
be higher than 14.2 MHz.
33.5

OTG dual role device (DRD)

1. External voltage regulator only needed when building a VBUS powered device.
2. STMPS2141STR needed only if the application has to support a VBUS powered device. A basic power
switch can be used if 5 V are available on the application board.
33.5.1

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 cable, depending on whether a MicroA or
MicroB plug 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 in section 4.2.4:
ID pin of the On-the-Go specification Rev2.0, 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_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 4.2.4: ID pin of the On-
the-Go specification Rev2.0, supplement to the USB2.0.
supply during USB operations.
BUS
pulsing method circuit used to charge/discharge V

Figure 396. OTG_FS A-B device connection

USB on-the-go full-speed (OTG_FS)
RM0430 Rev 8
through resistors during
BUS
1137/1324
1283