RM0090: Reference manual - STMicroelectronics

USB on-the-go high-speed (OTG_HS) RM0090
DP/DM. Pull-up and pull-down resistors are dynamically switched when the peripheral
role is changed via the host negotiation protocol (HNP).
● Pull-up/pull-down resistor ECN circuit
The DP pull-up consists of 2 resistors controlled separately from the OTG_HS as per
the resistor Engineering Change Notice applied to USB Rev2.0. The dynamic trimming
of the DP pull-up strength allows to achieve a better noise rejection and Tx/Rx signal
quality.
● VBUS sensing comparators with hysteresis used to detect VBUS_VALID, A-B Session
Valid and session-end voltage thresholds. They are used to drive the session request
protocol (SRP), detect valid startup and end-of-session conditions, and constantly
monitor the VBUS supply during USB operations.
● VBUS pulsing method circuit used to charge/discharge VBUS through resistors during
the SRP (weak drive).
Caution: To guarantee a correct operation for the USB OTG HS peripheral, the AHB frequency
should be higher than 30 MHz.
31.4 OTG dual-role device
31.4.1 ID line detection
The host or peripheral (the default) role depends on the level of the ID input line. It is
determined when the USB cable is plugged in and depends 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_HS conforms to the FSM standard described in
section 6.8.2. On-The-Go B-device of the USB On-The-Go Supplement, Revision 1.3.
● If the A-side of the USB cable is connected with a grounded ID, the OTG_HS issues an
ID line status change interrupt (CIDSCHG bit in the OTG_HS_GINTSTS register) for
host software initialization, and automatically switches to host role. In this configuration
the OTG_HS conforms to the FSM standard described by section 6.8.1: On-The-Go A-
Device of the USB On-The-Go Supplement, Revision 1.3.
31.4.2 HNP dual role device
The HNP capable bit in the Global USB configuration register (HNPCAP bit in the OTG_HS_
GUSBCFG register) configures the OTG_HS core to dynamically change from A-host to Adevice
role and vice-versa, or from B-device to B-host role and vice-versa, according to the
host negotiation protocol (HNP). The current device status is defined by the combination of
the Connector ID Status bit in the Global OTG control and status register (CIDSTS bit in
OTG_HS_GOTGCTL) and the current mode of operation bit in the global interrupt and
status register (CMOD bit in OTG_HS_GINTSTS).
The HNP programming model is described in detail in Section 31.13: OTG_HS
programming model.
31.4.3 SRP dual-role device
The SRP capable bit in the global USB configuration register (SRPCAP bit in
OTG_HS_GUSBCFG) configures the OTG_HS core to switch V BUS off for the A-device in
1159/1416 Doc ID 018909 Rev 3