Full-Speed Otg Phy - ST STM32L4x6 Reference Manual

RM0351
The USB protocol layer is driven by the serial interface engine (SIE) and serialized over the
USB by the transceiver module within the on-chip physical layer (PHY).
43.4.3

Full-speed OTG PHY

The embedded full-speed OTG PHY is controlled by the OTG FS core and conveys USB
control & data signals through the full-speed subset of the UTMI+ Bus (UTMIFS). It provides
the physical support to USB connectivity.
The full-speed OTG PHY includes the following components:
•
FS/LS transceiver module used by both host and device. It directly drives transmission
and reception on the single-ended USB lines.
•
integrated ID pull-up resistor used to sample the ID line for A/B device identification.
•
DP/DM integrated pull-up and pull-down resistors controlled by the OTG_FS core
depending on the current role of the device. As a peripheral, it enables the DP pull-up
resistor to signal full-speed peripheral connections as soon as V
a valid level (B-session valid). In host mode, pull-down resistors are enabled on both
DP/DM. Pull-up and pull-down resistors are dynamically switched when the device's
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_FS as per the resistor Engineering Change Notice applied to
USB Rev2.0. The dynamic trimming of the DP pull-up strength allows for better noise
rejection and Tx/Rx signal quality.
•
V
BUS
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 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.
sensing comparators with hysteresis used to detect V
supply during USB operations.
BUS
pulsing method circuit used to charge/discharge V
DocID024597 Rev 3
USB on-the-go full-speed (OTG_FS)
is sensed to be at
BUS
Valid, A-B Session
BUS
through resistors during
BUS
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