DS_6612_001
78M6612 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 78M6612 will always wake up in mission mode when system power is restored.
Additionally, the part will wake up in BROWNOUT mode when a timeout of the wake-up timer occurs.
2.5.1 Wake on Timer
If the part is in SLEEP or LCD mode, it can be awakened by the wake-up timer. 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 crystal 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
2.5 seconds (WAKE_RES=0). WAKE_PRD[2:0] selects a duration of from 1 to 7 LSBs.
The timer is armed by WAKE_ARM=1. It must be armed at least three RTC cycles before SLEEP or
LCD_ONLY is initiated. Setting WAKE_ARM presets the timer with the values in WAKE_RES and
WAKE_PRD and readies the timer to start when the MPU writes to SLEEP or LCD_ONLY. The timer is
reset and disarmed whenever the MPU is awake. Thus, if it is desired to wake the MPU periodically
(every 5 seconds, for example) the timer must be rearmed every time the MPU is awakened.
2.6 Data Flow
The data flow between CE and MPU is shown in Figure 25. In a typical application, the 32-bit compute
engine (CE) sequentially processes the samples from the voltage inputs on pins IA, VA, IB, and VB,
performing calculations to measure active power (Wh), reactive power (VARh), A2h, and V2h for four-
quadrant measurement. These measurements are then accessed by the MPU, processed further and
output using the peripheral devices available to the MPU.
Pulses
IRQ
Processed
Metering
Data
CE
MPU
Samples
Data
Pre-
Processor
Post-
Processor
I/O RAM (Configuration RAM)
Figure 25: MPU/CE Data Flow
Rev. 1.2
61
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