71M6533 Datasheet, PDF (63/124 Pages) Teridian Semiconductor Corporation – Energy Meter IC

FDS_6533_6534_004
71M6533/71M6534 Data Sheet
If there is no battery when system power returns, the part will switch to MISSION mode when PLL_OK
rises. All configuration bits will be in reset state, and RTC and MPU RAM data will be unknown and must
be initialized by the MPU.
2.5 Wake Up Behavior
As described above, the part will always wake up in MISSION mode when system power is restored. Ad-
ditionally, the part will wake up in BROWNOUT mode when PB rises (push button is pressed) or when a
timeout of the wake-up timer occurs.
2.5.1 Wake on PB
If the part is in SLEEP or LCD mode, it can be awakened by a rising edge on the PB pin. This pin is nor-
mally pulled to GND and can be pulled high by a push button depression. Before the PB signal rises, the
MPU is in reset due to WAKE being low. When PB rises, WAKE rises and within three crystal cycles, the
MPU begins to execute. The MPU can determine whether the PB signal woke it up by checking the
IE_PB flag. Figure 27 shows the Wake Up timing.
For debouncing, the PB pin is monitored by a state machine operating from a 32 Hz clock. This circuit will
reject between 31 ms and 62 ms of noise. Detection hardware will ignore all transitions after the initial
rising edge. This will continue until the MPU clears the IE_PB bit.
System
Power
(V3P3SYS)
PB or wake-
up timer
WAKE
15 CK32
cycles
MPU Mode
LCD
BROWNOUT
PLL_OK
time
Figure 27: Wake Up Timing
2.5.2 Wake on Timer
The wake-up timer can wake up the part if it is in SLEEP or LCD mode. Until this timer times out, the
MPU is in reset due to WAKE being low. When the wake-up timer times out, the WAKE signal rises and
within three CK32 cycles, the MPU begins to execute. The MPU can determine whether the timer woke it
by checking the AUTOWAKE interrupt flag (IE_WAKE).
The wake-up timer begins timing when the part enters LCD or SLEEP mode. Its duration is controlled by
WAKE_PRD[2:0] and WAKE_RES. WAKE_RES selects a timer LSB of either 1 minute (WAKE_RES = 1) or
2.0 seconds (WAKE_RES = 0).
When WAKE_RES = 0, the first wake-timer LSB may be 1.5 or 2.5 seconds; subsequent LSBs will be 2.0
seconds. WAKE_PRD[2:0] selects a duration of from 1 to 7 LSBs. When WAKE_RES = 0, the wake-up
timer duration will range from 1.5 + 2.0 *(WAKE_PRD[2:0] -1) seconds to 2.5 + 2.0 *(WAKE_PRD[2:0] -1)
seconds.
When WAKE_RES = 1, the time will be (WAKE_PRD[2:0] +1) minutes.
The timer is armed by WAKE_ARM = 1. It must be armed at least 64 RTC cycles (64 CK32 cycles), or 2
ms, before SLEEP or LCD_ONLY is initiated to ensure that WAKE_ARM is valid before entering the SLEEP
or LCD modes. Setting WAKE_ARM presets the timer with the values in WAKE_RES and WAKE_PRD and
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