ADE7566ASTZF8-RL2 AD [Analog Devices], ADE7566ASTZF8-RL2 Datasheet - Page 111

• Manufacturer Part Number: ADE7566ASTZF8-RL2
• Description: Single-Phase Energy Measurement IC with 8052 MCU, RTC, and LCD Driver
• Manufacturer: AD [Analog Devices]

Preliminary Technical Data
Take care when changing the interval timer time base. The
recommended procedure is as follows:
1.
2.
3.
4.
The RTC alarm event wakes the 8052 MCU core if the MCU is
in PSM2 when the alarm event occurs.
RTC CALIBRATION
The RTC provides registers to calibrate the nominal external
crystal frequency and its variation over temperature. A frequency
error up to ±248 ppm can be calibrated out by the RTC circuitry,
which adds or subtracts pulses from the external crystal signal.
The nominal crystal frequency should be calibrated with the
RTC nominal compensation register so that the clock going into
the RTC is precisely 32.768 kHz at 25°C. The RTC Temperature
Compensation SFR (TEMPCAL, 0xF7) is used to compensate
for the external crystal drift over temperature by adding or
subtracting additional pulses based on temperature.
The LSB of each RTC compensation register represents a
±2 ppm frequency error. The RTC compensation circuitry adds
the RTC Temperature Compensation SFR (TEMPCAL, 0xF7)
and the RTC Nominal Compensation SFR (RTCCOMP, 0xF6)
to determine how much compensation is required. Note that
the sum of these two registers is limited to ±248 ppm.
Calibration Flow
A RTC calibration pulse output is provided on the P0.2/CF1/
RTCCAL pin. Enable the RTC output by setting the RTCCAL
bit in the Interrupt Pins Configuration SFR (INTPR, 0xFF).
The RTC calibration is accurate to within ±2 ppm over a 30.5 sec
window in all operational modes: PSM0, PSM1, and PSM2. Two
output frequencies are offered for the normal RTC mode: 1 Hz
If the Alarm Interval SFR (INTVAL, 0xA6) is going to
be modified, write to this register first. Then, wait for
one 128 Hz clock cycle to synchronize with the RTC,
64,000 cycles at a 4.096 MHz instruction cycle clock.
Disable the interval timer by clearing the ITEN bit in the
RTC Configuration SFR (TIMECON, 0xA1). Then, wait
for one 128 Hz clock cycle to synchronize with the RTC,
64,000 cycles at a 4.096 MHz instruction cycle clock.
Read the RTC Configuration SFR (TIMECON, 0xA1) to
ensure that the ITEN bit is clear. If it is not, wait for
another 128 Hz clock cycle.
Set the time-base bits (ITS[1:0]) in the RTC Configuration
SFR (TIMECON, 0xA1) to configure the interval. Wait for
a 128 Hz clock cycle for this change to take effect.
Rev. PrA | Page 111 of 136
with FSEL[1:0] = 00 and 512 Hz with FSEL[1:0] = 01 in the
Interrupt Pins Configuration SFR (INTPR, 0xFF).
A shorter window of 0.244 sec is offered for fast calibration
during PSM0 or PSM1. Two output frequencies are offered for
this RTC calibration output mode: 500 Hz with FSEL[1:0] = 10
and 16.384 kHz with FSEL[1:0] = 11 in the Interrupt Pins
Configuration SFR (INTPR, 0xFF). Note that for the 0.244 sec
calibration window, the RTC is clocked 125 times faster than in
normal mode, resulting in timekeeping registers that represent
seconds/125, minutes/125 and hours/125 instead of seconds,
minutes, and hours. Therefore, this mode should be used for
calibration only.
Table 126. RTC Calibration Options
Option
Normal Mode 0
Normal Mode 1
Calibration Mode 0
Calibration Mode 1
When no RTC compensation is applied, that is, when RTC
Nominal Compensation SFR (RTCCOMP, 0xF6) and RTC
Temperature Compensation SFR (TEMPCAL, 0xF7) are equal
to 0, the nominal compensation required to account for the
error in the external crystal can be determined. In this case, it is
not necessary to wait for an entire calibration window to determine
the error in the pulse output. Calculating at the error in frequency
between two consecutive pulses on the P0.2/CF1/RTCCAL pin
is enough.
The value to write to the RTC Nominal Compensation SFR
(RTCCOMP, 0xF6) is calculated from the % error or seconds
per day error on the frequency output. Each LSB of the RTC
Nominal Compensation SFR (RTCCOMP, 0xF6) represents
2 ppm of correction where 1 sec/day error is equal to 11.57 ppm.
During calibration, user software writes the RTC with the
current time. Refer to the Read and Write Operations section
for more information on how to read and write the RTC
timekeeping registers.
RTCCOMP
RTCCOMP
=
=
5000
2
FSEL[1:0]
00
01
10
11
×
11
1
×
.
57
(%
×
Error
(
sec/day
Calibration
Window (sec)
30.5
30.5
0.244
0.244
ADE7566/ADE7569
)
Error
)
f
(Hz)
1
512
500
16,384
RTCCAL