VIPER
Power and power management
UART power management
COM4 and COM5 are generated from an external Exar XR16C2852 DUART. This
device supports a sleep mode with an auto wake up. By enabling this feature the
DUART enters sleep mode when there are no interrupts pending. The part resumes
normal operation when any of the following occur:
Receive data start bit.
•
•
•
Change of state on: CTS, DSR, CD, RI
Data is being loaded into transmit FIFO.
If the part is awakened by one of the above conditions, it returns to the sleep mode
automatically after the condition has cleared. Please see the XR16C2852 datasheet on
the Development Kit CD for information on enabling the sleep mode. Placing the
XR16C2852 into low power mode can reduce the power consumption of the VIPER by
2mA (10mW).
GPIO12 and GPIO13 on the PXA255 can be used to power down the RS232 drivers on
the VIPER, to save power. The following table shows the affect of GPIO12 and GPIO13
on the RS232 drivers. Placing the drivers in shutdown mode can reduce the power
consumption of the VIPER by up to 57mA (285mW).
GPIO12 GPIO13 Operation
Status
Transmitters Receivers
0 0 Normal
Operation Active Active
0 1 Receiver
Disabled Active High-Z
1 X Shutdown
High-Z High-Z
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 to 123mA (615mW). 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.
© 2004 Arcom Issue H
57
