71M6533 Datasheet, PDF (62/124 Pages) Teridian Semiconductor Corporation – Energy Meter IC

71M6533/71M6534 Data Sheet
FDS_6533_6534_004
VBAT
Battery
Current
MPU Mode
BROWNOUT
MPU Clock
Source
WAKE
Xtal
14.5 CK32
cycles
PLL_OK
Internal
RESETZ
1024 CK32
cycles
VBAT_OK
time
Figure 26: Power-Up Timing with VBAT only
2.4 Fault and Reset Behavior
2.4.1 Reset Mode
When the RESET pin is pulled high, all digital activity stops. The oscillator and RTC module continue to
run. Additionally, all I/O RAM 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 will continue to provide power to the
digital section.
Once initiated, the reset mode will persist until the reset timer times out, signified by WAKE rising. This
will occur in 4100 cycles of the real time clock after RESET goes low, at which time the MPU will begin
executing its pre-boot and boot sequences from address 00. See the description of Program Security
in Section 1.4.5 for additional descriptions of pre-boot and boot.
If system power is not present, the reset timer duration will be 2 cycles of the crystal clock at which time
the MPU will begin executing in BROWNOUT mode, starting at address 00.
2.4.2 Power Fault Circuit
The 71M6533 and 71M6534 includes a comparator to monitor system power fault conditions. When the
output of the comparator falls (V1<VBIAS), the I/O RAM bits PLL_OK are zeroed and the part switches to
BROWNOUT mode if a battery is present. Once system power returns, the MPU remains in reset and
does not transition to MISSION mode until 2048 to 4096 CK32 clock cycles later, when PLL_OK rises. If
a battery is not present, as indicated by BAT_OK=0, WAKE will fall and the part will enter SLEEP mode.
There are several conditions the device could be in as system power returns. If the part is in
BROWNOUT mode, it will automatically switch to MISSION mode when PLL_OK rises. It will receive an
interrupt indicating this. No configuration bits will be reset or reconfigured during this transition.
If the part is in LCD or SLEEP mode when system power returns, it will also switch to MISSION mode
when PLL_OK rises. In this case, all configuration bits will be in the reset state due to WAKE having
been zero. The RTC clock will not be disturbed, but the MPU RAM must be re-initialized. The hardware
watchdog timer will become active when the part enters MISSION mode.
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