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ADE7566/ADE7569/ADE7166/ADE7169

Rev. A | Page 116 of 144

REAL-TIME CLOCK

The ADE7566/ADE7569/ADE7166/ADE7169 have an

embedded real-time clock (RTC) as shown in

RTC REGISTERS

Figure 101. The

external 32.768 kHz crystal is used as the clock source for the

RTC. Calibration is provided to compensate the nominal crystal

frequency and for variations in the external crystal frequency

over temperature. By default, the RTC is maintained active in all

power saving modes. The RTC counters retain their values

through watchdog resets and external resets. They are only reset

during a power-on reset.

Note that all the real-time clock SFRs are not bit addressable.

Table 119. Real-Time Clock SFR

SFR

Address

Description

TIMECON

0xA1

RTC Configuration (see Table 120).

HTHSEC

0xA2

Hundredths of a Second Counter

(see Table 121).

8-BIT

PRESCALER

SECOND COUNTER

SEC

MINUTE COUNTER

MIN

HOUR COUNTER

HOUR

ITEN

ALARM

EVENT

8-BIT

INTERVAL COUNTER

INTVAL SFR

INTERVAL

TIMEBASE

SELECTION

MUX

RTCEN

32.768kHz

CRYSTAL

ITS1 ITS0

EQUAL?

CALIBRATION

RTCCOMP

TEMPCAL

MIDNIGHT EVENT

CALIBRATED

32.768kHz

HUNDREDTHS COUNTER

HTHSEC

Figure 101. RTC Implementation

SEC

0xA3

Seconds Counter (see Table 122).

MIN

0xA4

Minutes Counter (see Table 123).

HOUR

0xA5

Hours Counter (see Table 124).

INTVAL

0xA6

Alarm Interval (see Table 125).

RTCCOMP

0xF6

RTC Nominal Compensation

(see Table 126).

TEMPCAL

0xF7

RTC Temperature Compensation

(see Table 127).

Protecting the RTC from Runaway Code

To protect the RTC from runaway code, a key must be written

to the KYREG register to obtain write access to the Interrupt

Pins Configuration SFR (INTPR, 0xFF), Hundredths of a

Second Counter SFR (HTHSEC, 0xA2), Seconds Counter SFR

(SEC, 0xA3), Minutes Counter SFR (MIN, 0xA4), and Hours

Counter SFR (HOUR, 0xA5). KYREG should be set to 0xEA to

unlock it and reset it to zero after a timekeeping register is

written to. The RTC registers can be written using the following

8052 assembly code:

MOV

KYREG,#0EAh

MOV

INTPR,#080h

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