OM11077 NXP Semiconductors, OM11077 Datasheet - Page 335

• Manufacturer Part Number: OM11077
• Description: MODULE DIMM LPC2478 ARM7
• Manufacturer: NXP Semiconductors

Specifications of OM11077

• Accessory Type: Module Card
• For Use With/related Products: ARM-57TS-LPC2478
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 568-4742

NXP Semiconductors
UM10237_4
User manual
8.1 Power requirements
8.2 Clocks
8.3 Power management support
The USB protocol insists on power management by the device. This becomes very critical
if the device draws power from the bus (bus-powered device). The following constraints
should be met by a bus-powered device:
The USB device controller clocks are shown in
Table 292. USB device controller clock sources
To help conserve power, the USB device controller automatically disables the AHB master
clock and usbclk when not in use.
When the USB Device Controller goes into the suspend state (bus is idle for 3 ms), the
usbclk input to the device controller is automatically disabled, helping to conserve power.
However, if software wishes to access the device controller registers, usbclk must be
active. To allow access to the device controller registers while in the suspend state, the
USBClkCtrl and USBClkSt registers are provided.
When software wishes to access the device controller registers, it should first ensure
usbclk is enabled by setting DEV_CLK_EN in the USBClkCtrl register, and then poll the
corresponding DEV_CLK_ON bit in USBClkSt until set. Once set, usbclk will remain
enabled until DEV_CLK_EN is cleared by software.
When a DMA transfer occurs, the device controller automatically turns on the AHB master
clock. Once asserted, it remains active for a minimum of 2 ms (2 frames), to help ensure
that DMA throughput is not affected by turning off the AHB master clock. 2 ms after the
last DMA access, the AHB master clock is automatically disabled to help conserve power.
If desired, software also has the capability of forcing this clock to remain enabled using the
USBClkCtrl register.
Note that the AHB slave clock is always enabled as long as the PCUSB bit of PCONP is
set. When the device controller is not in use, all of the device controller clocks may be
disabled by clearing PCUSB.
The USB_NEED_CLK signal is used to facilitate going into and waking up from chip
Power-down mode. USB_NEED_CLK is asserted if any of the bits of the USBClkSt
register are asserted.
Clock source
AHB master clock
AHB slave clock
usbclk
1. A device in the non-configured state should draw a maximum of 100 mA from the bus.
2. A configured device can draw only up to what is specified in the Max Power field of
3. A suspended device can draw a maximum of 500 μA.
the configuration descriptor. The maximum value is 500 mA.
Rev. 04 — 26 August 2009
Description
Clock for the AHB master bus interface and DMA
Clock for the AHB slave interface
48 MHz clock from the USB clock divider, used to recover the
12 MHz clock from the USB bus
Chapter 13: LPC24XX USB device controller
Table 13–292
UM10237
© NXP B.V. 2009. All rights reserved.
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