ADE5166_08 AD [Analog Devices], ADE5166_08 Datasheet - Page 112

• Manufacturer Part Number: ADE5166_08
• Description: Single-Phase Energy Measurement IC with 8052 MCU, RTC, and LCD Driver
• Manufacturer: AD [Analog Devices]

ADE5166/ADE5169
REAL-TIME CLOCK (RTC)
The ADE5166/ADE5169 have an embedded RTC (see Figure 98).
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 fre-
quency over temperature. By default, the RTC is active in all the
power saving modes. The RTC counters retain their values
through watchdog resets and external resets and are reset only
during a power-on reset.
The ADE5166/ADE5169 provide two ways to access the RTC
data: by direct access through SFRs for configuration and by
indirect access through address and data SFRs for the timekeeping
registers and some other configurations. The address and data
SFRs act as pointers to the RTC internal registers.
ACCESS TO RTC SFRs
Access to the RTC SFRs is achieved by reading or writing to the
SFR addresses that are detailed in the Access to Internal RTC
Registers section. Writing to the indirect registers is protected
by a key, as explained in the Writing to Internal RTC Registers
section. Reading is not protected.
ACCESS TO INTERNAL RTC REGISTERS
Access to the internal RTC measurement registers is achieved by
writing to the RTC pointer address SFR (RTCPTR, Address 0xA3).
The RTCPTR register selects the RTC register to be accessed
and determines if a read or a write is performed (see Table 129).
Writing to Internal RTC Registers
The RTC circuitry runs off a 32.768 kHz clock. The timekeeping
registers, HTHSEC, SEC, MIN, HOUR, DAY, DATE, MONTH,
and YEAR are updated with a 32.768 kHz clock. However, the
TIMECON (Address 0xA1) and TIMECON2 (Address 0xA2)
SFRs and the INTVAL register (Address 0x09) are updated with
a 128 Hz clock. It takes up to two 128 Hz clock cycles from when
the MCU writes the TIMECON, TIMECON2, or INTVAL SFRs
until they are successfully updated in the RTC.
When the RTCW_RB bit of the RTCPTR SFR (Address 0xA3)
is set, the content of the RTCDAT SFR (Address 0xA4) is
transferred to the internal RTC register designated by the
address in the RTCPTR SFR. To protect the RTC timekeeping
registers from runaway code, a key must be written to the
KYREG SFR (Address 0xC1) to obtain write access to any of the
RTC indirect registers. The KYREG should be set to 0xEA to
unlock the timekeeping registers and is reset to zero after a
timekeeping register is written.
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The RTC registers can be written using the following 8052
assembly code:
MOV
CALL
…
UpdateRTC:
MOV
MOV
MOV
MOV
MOV
MOV
MOV
MOV
MOV
MOV
RET
Reading Internal Energy Measurement Registers
When Bit 7 of the RTCPTR SFR is cleared, the content of the
internal RTC data register designated by the address in RTCPTR
is transferred to the RTCDAT SFR. The RTC cannot be stopped
to read the current time because stopping the RTC introduces
an error in its timekeeping. Therefore, the RTC is read on-the-fly,
and the counter registers must be checked for overflow. This
can be accomplished using the following 8052 assembly code:
ReadAgain:
MOV
0
MOV
MOV
MOV
MOV
MOV
MOV
MOV
MOV
MOV
CJNE
Bank 0
RTCKey, #0EAh
UpdateRTC
KYREG, RTCKey
RTCDAT, #30
RTCPTR, #82h
KYREG, RTCKey
RTCDAT, #05
RTCPTR, #83h
KYREG, RTCKey
RTCDAT, #04
RTCPTR, #84h
RTCKey, #00h
RTCPTR #01
R0, RTCDAT
RTCPTR, #02
R1, RTCDAT
RTCPTR, #03
R2, RTCDAT
RTCPTR, #04
R3, RTCDAT
RTCPTR, #01
A, RTCDAT
A, 00h, ReadAgain
; Read HTHSEC using Bank
; Read SEC
; Read MIN
; Read HOUR
; Read HTHSEC
; 00h is R0 in