Rainbow Electronics 78M6631 - Manual (Page 7)

DS_6631_056 78M6631 Data Sheet
Rev 1 7
1.2 Device Reset
When the RESET pin is pulled high, all digital activity stops. Only the oscillator and RTC module continue
to run. Additionally, all IORAM bits are set to their default states. As long as V1 (the input voltage at the
power fault block) is greater than VBIAS, the internal 2.5 V regulator continues to provide power to the
digital section.
Once initiated, the reset mode persists until the reset timer times out. This occurs in 4096 cycles of the
crystal clock after RESET goes low, at which time the MPU begins executing its preboot and boot
sequences from address 0x0000.
1.3 Power Management
1.3.1 Voltage Regulator
The 78M6631 provides an on-chip voltage regulator to create a 2.5 V supply for the digital logic. This
regulator can be run off of the V3P3SYS or VBAT inputs depending upon power availability.
1.3.2 Power Fault Management
The 78M6631 provides for both hardware and software controlled power fault management. The V1 pin is
connected to a comparator to monitor system power fault conditions. When the input to the comparator
falls (V1 < VBIAS) the device can enter a BROWNOUT mode, if supported in firmware and there is
sufficient voltage on VBAT, that reduces the MPU rate to 32 kHz and disables all the measurement front-
end circuits. If the overhead on VBAT is insufficient to maintain a BROWNOUT mode, then the device can
also attempt to enter a SLEEP mode where only RTC functions are active.
If there is not sufficient voltage on VBAT (or it is not supported), then the part enters RESET mode when
the comparator fails.