71M6521DE/71M6521FE
Energy Meter IC
DATASHEET
JANUARY 2008
R1
R3
V3P3
GND
5kΩ
V1
C1
R2
100pF
Figure 37: Voltage Divider for V1
Even though a functional meter will not necessarily need a reset switch, it is useful to have a reset pushbutton for prototyping,
as shown in Figure 38, left side. The RESET signal may be sourced from V3P3SYS (functional in MISSION mode only),
V3P3D (MISSION and BROWNOUT modes), VBAT (all modes, if battery is present), or from a combination of these sources,
depending on the application. For a production meter, the RESET pin should be protected by the external components shown
in Figure 38, right side. R1 should be in the range of 100Ω and mounted as closely as possible to the IC.
Since the 71M6521DE/FE generates its own power-on reset, a reset button or circuitry, as shown in Figure 38, left
side, is only required for test units and prototypes.
VBAT/
V3P3D
71M6521
71M6521
V3P3D
R2
1kΩ
Reset
Switch
RESET
RESET
100Ω
R1
10kΩ
R1
0.1nF
DGND
DGND
Figure 38: External Components for RESET: Development Circuit (Left), Production Circuit (Right)
Connecting the Emulator Port Pins
Capacitors to ground must be used for protection from EMI. Production boards should have the ICE_E pin connected to
ground.
If the ICE pins are used to drive LCD segments, the pull-up resistors should be omitted, as shown in Figure 39, and 22pF
capacitors to GNDD should be used for protection from EMI.
It is important to bring out the ICE_E pin to the programming interface in order to create a way for reprogramming
parts that have the flash SECURE bit (SFR 0xB2[6]) set. Providing access to ICE_E ensures that the part can be reset
between erase and program cycles, which will enable programming devices to reprogram the part. The reset required is im-
plemented with a watchdog timer reset (i.e. the hardware WDT must be enabled).
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