71M6531D Datasheet, PDF (60/115 Pages) Teridian Semiconductor Corporation – Energy Meter IC

Data Sheet 71M6531D/F-71M6532D/F
FDS 6531/6532 005
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 25 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 25: Wake Up Timing
2.5.2 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 processor writes to SLEEP or LCD_ONLY. The timer is
reset and disarmed whenever the processor 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 the Compute Engine (CE) and the MPU is shown in Figure 26. In a typical appli-
cation, the 32-bit 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 metering. These measurements are then accessed by the MPU, processed further and output
using the peripheral devices available to the MPU. Figure 26 illustrates the CE/MPU data flow.
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