DS80C320-MCG Datasheet, PDF (91/175 Pages) Dallas Semiconductor – High-Speed Microcontroller User Guide

High-Speed Microcontroller User’s Guide
SECTION 7: POWER MANAGEMENT
The High-Speed Microcontroller has several features that relate to power consumption and management.
They provide a combination of controlled operation in unreliable power applications and reduced power
consumption in portable or battery powered applications. The range of features is shown below with
details to follow.
POWER MANAGEMENT
EARLY WARNING POWER FAIL INTERRUPT
POWER FAIL/POWER ON RESET
BAND–GAP SELECT
WATCHDOG WAKE UP FROM IDLE
POWER SAVING
IDLE MODE
STOP MODE
RING WAKE UP FROM STOP
POWER MANAGEMENT MODES
PRECISION VOLTAGE MONITOR
The High-Speed Microcontroller uses a precision band-gap reference and other analog circuits to monitor
the state of the power supply during power-up and power-down transitions. Other microcontroller
systems would require external circuits to perform these functions. The band-gap reference provides a
precise voltage to compare with V_CC. When V_CC begins to drop, the Power Monitor compares it to its
reference. This enables the analog circuits to detect when V_CC passes through predetermined thresholds,
V_PFW and V_RST. These are specified in the individual product data sheets.
EARLY WARNING POWER FAIL INTERRUPT
Devices which incorporate the precision voltage reference have the ability to generate a power-fail
interrupt and/or reset in response to a low supply voltage. When V_CC reaches the V_PFW threshold, the
microcontroller can generate an power-fail Interrupt. This early warning of supply voltage failure allows
the system time to save critical parameters in nonvolatile memory and put external functions in a safe
state.
The power-fail interrupt is optional and is enabled using the Enable Power Fail Warning Interrupt (EPFI)
bit at WDCON.5. If enabled, V_CC dropping below V_PFW will cause the device to vector to address 33h.
The Power-fail Interrupt status bit, PFI (WDCON.4), will be set anytime V_CC transitions below V_PFW.
This flag is not cleared when V_CC is above V_PFW, and software should clear it immediately after reading
it. As long as the condition exists, PFI will be immediately set again by hardware.
A typical application of the PFI is to place the device into a “safe mode” when a power loss appears
imminent. When the interrupt occurs, the code vectors to location 33h. At this time, software can disable
the interrupt, save any critical data, clear PFI, then continually poll the status of the power supply via the
PFI flag. As long as PFI is set, power is still below V_PFW. If power returns to the proper level, PFI will
not be set once cleared by software. This indicates a safe operating condition. If power continues to fall,
a power-fail reset will be invoked automatically.
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