Dallas Semiconductor's DS1239 MicroManager is a complete monitor for processor controlled systems, with the same functionality as the DS1236 and with an additional external power supply control function. A precision temperature-compensated reference and comparator continuously monitor the system power supply. If VCC levels breach threshold tolerance, an internal power-fail signal is generated which activates reset. When power returns to tolerance, the DS1236 holds reset for a minimum of 25ms (typically 100ms) while the power supply and processor stabilize. Optional threshold levels are available: the DS1236-5 and DS1236A-5 for resets at ±5% of a 5V supply; and the DS1236 and DS1236A for ±10% of a 5V supply. The watchdog timer circuitry monitors software execution. If a strobe input is not driven low prior to user-set timeouts between approximately 100ms and 600ms the timer forces a processor reset. To enable external override, the DS1236 debounces the pushbutton input and guarantees a minimum active reset pulse width of 25ms. A switch directs SRAM power between VCC or an external battery, whichever is greater. This switched supply can also back up a CMOS microprocessor. To enable write protection upon the detection of a power-fail condition, the chip enable output is held to within 0.3V VCC or to within 0.7V of battery input. The DS1239 facilitates the power-up and power-down sequencing of a main power supply from a keyboard or pushbutton with input and output power supply control pins. The DS1239 MicroManager is a complete system monitor for SRAM, microprocessor software, and systems power. The functions of power monitor, watchdog timer, power switching, write protection, and pushbutton reset are essential to reliable operation in battery-backed, processor-controlled systems. Integrated features also reduce component count, save power, simplify board layout, and save cost and space.