FDS 6531/6532 005
Data Sheet 71M6531D/F-71M6532D/F
When system power is not available (i.e. when V1<VBIAS), the 71M6531 will be in one of three battery
modes: BROWNOUT, LCD, or SLEEP mode. Figure 21 shows a state diagram of the various operation
modes, with the possible transitions between modes. For information on the timing of mode transitions
refer to Figure 22 through Figure 24.
RESET
MISSION
V3P3SYS
falls
V1 > VBIAS
V1 <= VBIAS
IE_PLLRISE
-> 1
IE_PLLFALL
-> 1
V3P3SYS
rises
V3P3SYS
rises
LCD_ONLY
BROWNOUT
V3P3SYS
rises
RESET &
VBAT_OK
IE_PB -> 1
IE_WAKE ->
1
PB
SLEEP or
VBAT_OK
timer
LCD
timer
PB
VBAT_OK
VBAT_OK
RESET &
VBAT_OK
SLEEP
Figure 21: Operation Modes State Diagram
When V1 falls below VBIAS or the part wakes up under battery power, the part will automatically enter
BROWNOUT mode (see Section 2.5 Wake-Up Behavior). From BROWNOUT mode, the part may enter
either LCD mode or SLEEP mode, as controlled by the MPU via the I/O RAM bits LCD_ONLY and SLEEP.
The transition from MISSION mode to BROWNOUT mode is signaled by the IE_PLLFALL interrupt flag
(SFR 0xE8[7]). The transition in the other direction is signaled by the IE_PLLRISE interrupt flag (SFR
0xE8[6]), when the PLL becomes stable.
Meters that do not require functionality in the battery modes, e.g. meters that only use the SLEEP
mode to maintain the RTC, still need to contain code that brings the chip from BROWNOUT
mode to SLEEP mode. Otherwise, the chip remains in BROWNOUT mode, once the system
power is missing, and consumes more current than intended.
Similarly, meters equipped with batteries need to contain code that transitions the chip to SLEEP
mode as soon as the battery is attached in production. Otherwise, remaining in BROWNOUT
mode would add unnecessary drain to the battery.
Transitions from both LCD and SLEEP mode are initiated by wake-up timer timeout conditions or push-
button events. When the PB pin is pulled high (pushbutton is pressed), the IE_PB interrupt flag (SFR
0xE8[4]) is set, and when the wake-up timer times out, the IE_WAKE interrupt flag (SFR 0xE8[5]) is set.
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