UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
686 of 1441
NXP Semiconductors
UM10503
Chapter 25: LPC43xx/LPC43Sxx USB0 Host/Device/OTG controller
25.7.5 ATX transceiver
The USB-OTG has a USB transceiver with UTMI+ interface. It contains the required
transceiver OTG functionality; this includes:
•
VBUS sensing for producing the session-valid and VBUS-valid signals.
•
sampling of the USB_ID input for detection of A-device or B-device connection.
•
charging and discharging of VBUS for starting and ending a session as B-device.
25.7.6 Modes of operation
In general, the USB-OTG can operate either in host mode or in device mode. Software
must put the core in the appropriate mode by setting the USBMODE.CM field (‘11’ for host
mode, ‘10’ for device mode).
The USBMODE.CM field can also be equal to ‘00’, which means that the core is in idle
mode (neither host nor device mode). This will happen after the following:
•
a hardware reset.
•
a software reset via the USBCMD.RST bit. When switching from host mode to device
mode as part of the HNP protocol (or vice versa), software must issue a software
reset which sets the USB core to the idle state in a time frame dependent on the
software.
25.7.7 SOF/VF indicator
See
for connecting the SOF signal to other peripherals on the LPC43xx.
The USB-OTG generates a SOF/VF indicator signal, which can be used by user specific
external logic.
In FS mode, the SOF/VF indicator signal has a frequency equal to the frame frequency,
which is about 1 kHz. The signal is high for half of the frame period and low for the other
half of the frame period. The positive edge is aligned with the start of a frame (= SOF).
In HS mode, the SOF/VF indicator signal has a frequency equal to the virtual frame
frequency. The positive edge indicates the start of the Virtual Frame and is aligned with
the occurrence of an SOF token on the USB
The length of the virtual frame is defined as: VF = microframe
2
bInterval
bInterval is specified in the 4-bit programmable BINTERVAL.BINT register field. The
minimum value of bInterval is 0, the maximum value is 15.
In suspend mode the SOF/VF indicator signal is turned off (= remains low).
25.7.7.1 SOF frame length adjust
Remark:
The SOF frame length adjust is implemented on parts with on-chip flash only.
If the USB is in host mode, the SOF length can be changed dynamically based on the
data flow. The frame length adjustment feature is useful when combining the USB with I2S
in an audio application where the audio clock is derived from a highly accurate source. In
this case, I2S is consuming the buffer at the audio clock rate while the USB is filling the
buffer. If software detects that the USB is filling the buffer slowly relative to the I2S
