UM10503
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© NXP B.V. 2012. All rights reserved.
User manual
Rev. 1.3 — 6 July 2012
582 of 1269
NXP Semiconductors
UM10503
Chapter 23: LPC43xx USB0 Host/Device/OTG controller
In the operational state both the transceiver clock and system clocks are running.
Software can initiate a low power mode autonomously by disconnecting from the host to
go into the disconnect state. Once in this state, the software can set the Suspend bit to
turn off the transceiver clock putting the system into the disconnect-Suspended state.
Since software cannot depend on the presence of a clock to clear the Suspend bit, a
wake-up event must be defined which would clear the suspend bit and allow the
transceiver clock to resume.
The device can also go into suspend mode as a result of a suspend command from the
host. Suspend is signaled on the bus by 3 ms of idle time on the bus. This will generate a
suspend interrupt to the software at which point the software must prepare to go into
suspend then set the suspend bit. Once the Suspend bit is set the transceiver clock may
turn off and the device will be in the suspended state. The device has two ways of getting
out of suspend.
1. If remote wake-up is enabled, a wake-up event could be defined which would clear
the Suspend bit. The software would then initiate the resume by setting the Resume
bit in the port controller then waiting for a port change interrupt indicating that the port
is in an operational state.
Fig 60. Device power state diagram
Host directed
Autonomous
operational
3 ms
idle
Low-power
request
resume
interrupt
received
prepare
for
Suspend
disconnect
SW sets
Suspend bit
SW sets
Suspend bit
user-defined
wakeup
disconnect
Suspend
Suspend
Resume
user-defined
wakeup
start
Resume
Lock power states
(clock may be suspended)