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VIPER Technical Manual Power and power management
© 2007 Eurotech Ltd Issue E 83
UART power management
COM4 and COM5 are generated from an external Exar XR16C2850 DUART. This
device supports a sleep mode. By enabling this feature the DUART enters sleep mode
when there are no interrupts pending. Please see the XR16C2850 datasheet on the
Development Kit CD for information on enabling the sleep mode.
GPIO12 on the PXA255 can be used to power down the RS232 transceivers on
COM1, 2, 3 and 4. The following table shows the affect of GPIO12 on the RS232
transceivers:
GPIO12 Operation status Transmitters Receivers
0 Normal operation Active Active
1 Shutdown High-Z High-Z
Placing the XR16C2850 and the RS232 transceivers into low power mode can reduce
the power consumption of the VIPER up to 25mA ±3mA (125mW ±15mW).
CompactFLASH power management
The power supply to the CompactFLASH interface is controlled via software, and
supports hot swap card insertion and CompactFLASH power down states. GPIO82 on
the PXA255 is used to control the power supply. Setting this line to logic ‘0’ switches off
power to the CompactFLASH interface.
Ethernet power management
The network interface supports a power down mode, which shuts down the internal
MAC and PHY blocks of the network controller. Placing the controller into low power
mode can reduce the power consumption of the VIPER by up to108mA ±3mA (540mW
±15mW). To power down the PHY write ‘1’ to the power down bit in the MII PHY
Register 0, Control Register. To power down the MAC write ‘1’ to the EPH PowerEN bit
in the Bank 1, Configuration Register. See the LAN91C111 datasheet contained on the
Development Kit CD for further details.
USB power management
The USB Host controller supports a USB suspend state. Placing the controller into the
USB suspend state can reduce the power consumption of the VIPER by up to 37mA
±3mA (185mW ±15mW). To suspend the USB, the software must write to the relevant
bits in the HcControl Register (81h). Please see the ISP1160 datasheet contained on
the Development Kit CD.
To wake the USB Host Controller from suspend, pulse GPIO13 high.
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