43.2.1 Data Structures
To efficiently manage USB endpoint communications, USBFS implements a Buffer
Descriptor Table (BDT) in system memory. See Figure 43-6.
43.2.2 On-chip transceiver required external components
USB system operation requires external components to ensure that driver output
impedance, eye diagram, and VBUS cable fault tolerance requirements are met. DM and
DP I/O pads must connect through series resistors (approximately 33 Ω each) to the USB
connector on the application printed circuit board (PCB). Additionally, signal quality
optimizes when these 33 Ω resistors are mounted closer to the processor than to the USB
board-level connector. The USB transceiver includes:
• An internal 1.5 kΩ pullup resistor on the USB_DP line for full-speed device
(controlled by USB_CONTROL[DPPULLUPNONOTG] or
USB_OTGCTL[DPHIGH])
• Internal 15 kΩ pulldown resistors on the USB_DP and USB_DM signals, which are
primarily intended for Host mode operation but are also useful in Device mode as
explained below.
NOTE
For device operation, the internal 15 kΩ pulldowns should
be enabled to keep the DP and DM ports in a known
quiescent state when the VBUS detection software
determines that the USB connection is not activated,
including the cases when no cable to a host is present or
when the USB port is not used. The internal 15 kΩ
pulldowns should be controlled by USB_CTRL[PDE] in
this case.
For host operation, the internal 15 kΩ pulldowns are
enabled automatically, as required by the USB 2.0
specification, when USB_CTL[HOSTMODEEN] is
asserted high.
The following diagrams provide overviews of host-only, device-only, and dual-role
connections, respectively. For more details, see the Kinetis Peripheral Module Quick
Reference(KQRUG).
Chapter 43 Universal Serial Bus Full Speed OTG Controller (USBFSOTG)
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
NXP Semiconductors 1073
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