问 选择MAX的DATASHEETS，供参考
The MAX706 provide four functions:
1) A reset output during power-up, power-down, and brownout conditions.
2) An independent watchdog output that goes low if the watchdog input
has not been toggled within 1.6 seconds.
3) A 1.25V threshold detector for power-fail warning, low-battery
detection, or for monitoring a power supply other than +5V.
4) An active-low manual-reset input.