STM32F101xx, STM32F102xx, STM32F103xx, STM32F105xx and ...

RM0008
USB on-the-go full-speed (OTG_FS)
within the USB data RAM. There is one Tx-FIFO push register for each in-endpoint
(peripheral mode) or out-channel (host mode).
The CPU receives the data from the USB by reading 32-bit words from dedicated OTG_FS
addresses (pop registers). The data are then automatically retrieved from a shared Rx-FIFO
configured within the 1.25 KB USB data RAM. There is one Rx-FIFO pop register for each
out-endpoint or in-channel.
The USB protocol layer is driven by the serial interface engine (SIE) and serialized over the
USB by the full-/low-speed transceiver module within the on-chip physical layer (PHY).
26.3.2 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 BUS is sensed to be at
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 Enginering 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 sensing comparators with hysteresis used to detect V BUS 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 V BUS supply during USB operations.
● V BUS pulsing method circuit used to charge/discharge V BUS through resistors during
the SRP (weak drive).
Doc ID 13902 Rev 9 697/995