71M6521BE
Energy Meter IC
DATA SHEET
JANUARY 2008
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 MPU RAM data will be unknown and must be initialized by the MPU.
Wake Up Behavior
As described above, the part will always wake up in mission mode when system power is restored. Additionally, the part will
wake up in BROWNOUT mode when PB rises (push button pressed) or when a timeout of the wake-up timer occurs.
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 normally 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.
For debouncing, the PB pin is monitored by a state machine operating from a 32Hz clock. This circuit will reject between 31ms
and 62ms 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
15 CK32
cycles
WAKE
MPU Mode
PLL_OK
LCD
BROWNOUT
time
Figure 25: Wake Up Timing
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 crystal clock 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.
V1.0
© 2005-2008 TERIDIAN Semiconductor Corporation
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