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Universal Serial Bus Interface – On-The-Go Module
10-6
Freescale Semiconductor
10.2.1
USB OTG Control and Status Signals
The USB OTG module uses a number of control and status signals to implement the OTG protocols. The
USB OTG module must be able to individually enable and disable the pull-up and pull-down resistors on
DP and DM, and it must be able to control and sense the levels on the USB VBUS line.
These control and status signals are implemented on chip as registers within the chip-configuration module
(CCM) to minimize the pin-count on the device. With firmware, the system designer uses an external
device to manage the OTG functions to implement communications across the I
2
C bus or GPIO pins.
The OTG controller status register (UOCSR) implements as follows:
•
Writes to the UOCSR register from the firmware set the corresponding bits on the USB interface.
•
When the USB OTG module outputs change, the corresponding bits on the UOCSR register are
updated, and a maskable interrupt is generated.
The UOCSR register is documented in the CCM chapter, see
Section 11.3.6, “USB On-the-Go Controller
ULPI_NXT
I
Next data. PHY asserts ULPI_NXT to throttle data. When USB port sends data to the PHY,
ULPI_NXT indicates when PHY accepts the current byte. The USB port places the next byte
on the data bus in the following clock cycle. When the PHY sends data to USB port, ULPI_NXT
indicates when a new byte is available for USB port to consume.
State
Meaning
Asserted—PHY is ready to transfer byte.
Negated—PHY is not ready.
Timing
Synchronous to ULPI_CLK.
ULPI_STP
O
Stop. ULPI_STP indicates the end of a transfer on the bus.
State
Meaning
Asserted—USB asserts this signal for one clock cycle to stop the data stream
currently on the bus. If the USB port sends data to the PHY, ULPI_STP
indicates the last data byte was previously on the bus. If the PHY is sending
data to the USB port, ULPI_STP forces the PHY to end its transfer, deassert
ULPI_DIR, and relinquish control of the data bus to the USB port.
Negated—Indicates normal operation.
Timing
Synchronous to USB_CLK or ULPI_CLK
ULPI_DATA[7:0]
I/O Data bit n. ULPI_DATAT
n
is bit
n
of the 8-bit, bi-directional data bus used to carry USB, register,
and interrupt data between the USB port controller and the PHY.
State
Meaning
Asserted—Data bit
n
is 1
.
Negated—Data bit
n
is 0.
Timing
Synchronous to USB_CLK or ULPI_CLK
Table 10-2. USB OTG Signal Descriptions (continued)
Signal
I/O
Description
Содержание MCF54455
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