Datasheet

ADE5166/ADE5169/ADE5566/ADE5569 Data Sheet
Rev. D | Page 120 of 156
PLL
The ADE5166/ADE5169/ADE5566/ADE5569 are intended for
use with a 32.768 kHz watch crystal. A PLL locks onto a multiple
of this frequency to provide a stable 4.096 MHz clock for the
system. The core can operate at this frequency or at binary
submultiples of it to allow power savings when maximum core
performance is not required. The default core clock is the PLL clock
divided by 4, or 1.024 MHz. The ADE energy measurement clock
is derived from the PLL clock and is maintained at 4.096/5 MHz
(or 819.2 kHz) across all CD settings.
The PLL is controlled by the CD bits in the power control SFR
(POWCON, Address 0xC5[2:0]). To prevent erroneous changes
to the POWCON SFR, a key is required to modify the register.
First, the key SFR (KYREG, Address 0xC1) is written with the
key, 0xA7, and then a new value is written to the POWCON SFR.
If the PLL loses lock, the MCU is reset and PLL_FLT is set in the
peripheral configuration SFR (PERIPH, Address 0xF4[4]). Set the
PLLACK bit in the start ADC measurement SFR (ADCGO,
Address 0xD8[7]) to acknowledge the PLL fault, clearing the
PLL_FLT bit.
PLL REGISTERS
Table 125. Power Control SFR (POWCON, Address 0xC5)
Bit Mnemonic Default Description
7 Reserved 1 Reserved.
6 METER_OFF 0 Set this bit to 1 to turn off the modulators and energy metering DSP circuitry to reduce power if
metering functions are not needed in PSM0.
5 Reserved 0 This bit should be kept at 0 for proper operation.
4 COREOFF 0 Set this bit to 1 to shut down the core if in the PSM1 operating mode.
3 Reserved Reserved.
[2:0] CD 010 Controls the core clock frequency (f
CORE
). f
CORE
= 4.096 MHz/2
CD
.
CD Result (f
CORE
in MHz)
000 4.096
001 2.048
010 1.024
011 0.512
100 0.256
101 0.128
110 0.064
111 0.032
Writing to the Power Control SFR (POWCON, Address 0xC5)
Note that writing data to the POWCON SFR involves writing 0xA7 into the key SFR (KYREG, Address 0xC1), followed by a write to the
POWCON SFR.
Table 126. Key SFR (KYREG, Address 0xC1)
Bit Mnemonic Default Description
[7:0] KYREG 0 Write 0xA7 to the KYREG SFR before writing to the POWCON SFR to unlock it.
Write 0xEA to the KYREG SFR before writing to the INTPR, HTHSEC, SEC, MIN, or HOUR timekeeping
registers to unlock them (see the RTC Registers section).