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USB Registers
1776
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Universal Serial Bus (USB) Controller
Table 27-80. USBLPMCNTRL Register Field Descriptions (OTG B / Device) (continued)
Bit
Field
Type
Reset
Description
3-2
LPMEN
R/W
0x0
LPM Enable.
This register is used to enable LPM in the USB. There are three
LPM levels which determine the response of the USB to LPM
transactions.
The three levels are:
0x0 = LPM and Extended transactions are not supported. In this
case, the USB does not respond to LPM transactions and LPM
transactions cause a time-out.
0x1 = LPM is not supported but extended transactions are
supported. In this case, the USB does respond to an LPM
transaction with a STALL.
0x2 = LPM and Extended transactions are not supported. In this
case, the USB does not respond to LPM transactions and LPM
transactions cause a time-out.
0x3 = The USB supports LPM extended transactions. In this case,
the USB responds with a NYET or an ACK as determined by the
value of TXLPM and other conditions.
1
RES
R/W
0x0
LPM Resume.
This bit is used by software to initiate resume (remote wakeup).
This bit differs from the classic RESUME bit in the USBPOWER
register (address 0x001), in that the RESUME signal timing is
controlled by hardware.
0x0 = No effect
0x1 = Resume signaling is asserted for 50 µs. This bit is self
clearing.
0
TXLPM
R/W
0x0
Transmit LPM Transaction Enable.
This bit is only effective if LPMEN is set to 0x3.
This bit can be set in the same cycle as LPMEN.
If this bit is set to 0x1 and LPMEN = 0x3, the USB can respond in
the following ways: If no data is pending (all TX FIFOs are empty),
the USB will respond with an ACK.
In this case, this bit self clears and a software interrupt is generated.
If data is pending (Data resides in at least one TX FIFO), the USB
responds with a NYET.
In this case, this bit does NOT self clear, however a software
interrupt is generated.
0x0 = No effect
0x1 = USB transitions to the L1 state upon the receipt of the next
LPM transaction.