M48T02-70PC1(1998) View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
M48T02-70PC1 Datasheet PDF : 15 Pages
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M48T02, M48T12
CLOCK OPERATION (cont’d)
The second approach is better suited to a manu-
facturing environment, and involves the use of
some test equipment. When the Frequency Test
(FT) bit, the seventh-most significant bit in the Day
Register, is set to a ’1’, and the oscillator is running
at 32,768 Hz, the LSB (DQ0) of the Seconds Reg-
ister will toggle at 512 Hz. Any deviation from 512
Hz indicates the degree and direction of oscillator
frequency shift at the test temperature. For exam-
ple, a reading of 512.01024 Hz would indicate a
+20 ppm oscillator frequency error, requiring a
-10(WR001010) to be loaded into the Calibration
Byte for correction. Note that setting or changing
the Calibration Byte does not affect the Frequency
test output frequency. The device must be selected
and address 7F9h must be held constant when
reading the 512 Hz on DQ0.
TheFT bit must be set using the same methodused
to set the clock, using the Write bit. The LSB of the
Seconds Register is monitored by holding the
M48T02/12 in an extended read of the Seconds
Register, without having the Read bit set. The FT
bit MUST be reset to ’0’ for normal clock operations
to resume.
For more information on calibration, see the Appli-
cation Note AN924 ”TIMEKEEPER Calibration”.
which stabilizes the VCC bus. The energy stored in
the bypass capacitors will be releasedas low going
spikes are generated or energy will be absorbed
when overshoots occur. A bypass capacitor value
of 0.1µF (as shown in Figure 12) is recommended
in order to provide the needed filtering.
In addition to transients that are caused by normal
SRAM operation, power cycling can generate
negative voltage spikes on VCC that drive it to
values below VSS by as much as one Volt. These
negative spikes can cause data corruption in the
SRAM while in battery backup mode. To protect
from these voltage spikes, it is recommeded to
connecta schottky diode from VCC to VSS (cathode
connected to VCC, anode to VSS). Schottky diode
1N5817 is recommended for through hole and
MBRS120T3 is recommended for surface mount.
Figure 12. Supply Voltage Protection
VCC
0.1µF
VCC
DEVICE
POWER SUPPLY DECOUPLING and UNDER-
SHOOT PROTECTION
ICC transients, including those produced by output
switching, can produce voltage fluctuations, result-
ing in spikes on the VCC bus. These transients can
be reduced if capacitors are used to store energy,
VSS
AI02169
12/15
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