Computer Hardware User Manual
ZEUS Technical Manual Power and power management
© 2007 Eurotech Ltd Issue D 73
COM Ports power management
RS232 transceivers can be placed in low power mode in case they are not used. This
can reduce the power consumption of each RS232 transceiver down to 33 μW. GPIO
pins 3 and 4 of Expander 2 (I2C address 0x22) are used to shut down COM1 and
COM2. GPIO pin 1 of Expander 1 (I2C address 0x21) is used to shut down COM3.
EXP2_GPIO3 (U1_RS232_SHDN#) COM1 RS232 operation status
0 Shutdown mode
1 Normal operation
EXP2_GPIO4 (U2_RS232_SHDN#) COM2 RS232 operation status
0 Shutdown mode
1 Normal operation
EXP1_GPIO1 (U3_RS232_EN) COM3 RS232 operation status
0 RS232 Shutdown mode
(RS422/485 enabled)
1 Normal operation
Temperature sensor power management
The LM75A device can be set to operate in two modes: normal or shut-down. In
normal operating mode, the temp-to-digital conversion is executed every 100ms and
the Temp register is updated at the end of each conversion. In shut-down mode, the
device becomes idle, data conversion is disabled and the Temp register holds the
latest result. However, the device I
2
C interface is still active and register write/ read
operation can be performed. The device operating mode is controllable by
programming bit B0 of the configuration register. The temperature conversion is
initiated when the device is powered-up or put back into normal mode from shut-down.
The power consumption in shut-down mode is near zero (11.5μW).
For more information about power management, refer to the LM75A
datasheet on the
Development Kit CD.
I/O expander power management
When the serial I
2
C interface is idle and the PWM intensity control is unused, the
MAX7313 automatically enters standby mode. If the PWM intensity control is used, the
operating current is slightly higher because the internal PWM oscillator is running. The
power consumption in standby mode (with PWM disabled) is near zero (4μW).
Configuration PROM power management
When the serial I
2
C interface is idle the 24AA01 automatically enters standby mode.
The power consumption in standby mode is near zero (3.3μW).