MicroMonitor Chip. PBRST 1. TOL 3. GND 4. See Mech. Drawings Section.
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All rights reserved. First, a precision temperature-compensated reference and comparator circuit monitors the status of VCC. When an out-of-tolerance condition occurs, an internal power fail signal is generated which forces reset to the active state.
When VCC returns to an in-tolerance condition, the reset signals are kept in the active state for a minimum of ms to allow the power supply and processor to stabilize. MicroMonitor is a trademark of Dallas Semiconductor. The DS debounces the pushbutton input and guarantees an active reset pulse width of ms minimum. The third function is a watchdog timer. The DS has an internal timer that forces the reset signals to the active state if the strobe input is not driven low prior to timeout.
The watchdog timer function can be set to operate on timeout settings of approximately ms, ms, and 1. On power-up, RST and RST are kept active for a minimum of ms to allow the power supply and processor to stabilize. The pushbutton reset input requires an active low signal.
The ms delay starts as the pushbutton reset input is released from low level. The time period is set by the TD input to be typically ms with TD connected to ground, ms with TD left unconnected, and 1.
If a high-to-low transition occurs on the ST input pin prior to timeout, the watchdog timer is reset and begins to timeout again. If the watchdog timer is allowed to timeout, then the RST and RST signals are driven to the active state for ms minimum. When the microprocessor is functioning normally, these signals would, as a matter of routine, cause the watchdog to be reset prior to timeout. To guarantee that the watchdog timer does not timeout, a high-to-low transition must occur at or less than the minimum shown in Table 1.
A typical circuit example is shown in Figure 3. All voltages referenced to ground. Measured with outputs open. RST is an open-drain output. Must not exceed tTD minimum. See Table 1. RST remains within 0. Watchdog can not be disabled.
It must be strobed to avoid resets.
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