ZEUS Technical Manual

Power and power management

 

 

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. GPIO97 on the PXA270 (signal CF_PWEN) is used to control the power supply switch. Setting this line to logic ‘0’ switches off the power to the CompactFlash interface. The current- limiting (1A) and thermal protection features of the power switch eliminate the need for the fuse. The power supply to the CompactFlash is derived from 3.3V supply.

CPU_ GPIO97 (CF_PWEN)CF power

0

Power off

1

Power on

 

 

Wireless modem power management

The power supply to the wireless modem interface (VCC_MODEM) is controlled by SYS_EN signal of the PXA270, and is switched off when PXA270 is in deep-sleep mode. The current-limiting (2A) and thermal protection features of the power switch eliminate the need for the fuse. VCC_MODEM power supply is derived from the ZEUS +5V supply.

GSM_ON and GPS_ON control signals are provided on the ZEUS Modem connector (J23). They are controlled by on-board GPIO expander (see On-Board GPIO expanders pin assignments, page 29). For details on how to use these signals, and other power management features of the specific wireless and GPS devices, please consult the datasheet of the device used.

USB power management

A USB power control switch controls the power, and protects against short-circuit and over-current conditions, on USB host ports.

If the USB voltage VBUSx is short-circuited, or more than 500mA is drawn from any VBUSx supply, the switch turns off the power supply and protects the device and board automatically. The VBUSx power supplies are derived from the ZEUS +5V supply.

The following table shows the PXA270 assignments for power enable and over-current signals:

Host 1/2 functions PXA270 GPIO

Active

USB_PWE1 GPIO89 High

USB_OC1# GPIO88 Low

USB_PWE2 GPIO22 High

USB_OC2# GPIO114 Low

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