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M48Z129Y Datasheet(PDF) 4 Page - STMicroelectronics

Part No. M48Z129Y
Description  3.3V/5V 1 Mbit 128Kb x8 ZEROPOWER SRAM
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Maker  STMICROELECTRONICS [STMicroelectronics]
Homepage  http://www.st.com

M48Z129Y Datasheet(HTML) 4 Page - STMicroelectronics

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M48Z129Y, M48Z129V
Note: A power failure during a write cycle may
corrupt data at the current addressed location, but
does not jeopardize the rest of the RAM’s content.
At voltages below VPFD(min), the memory will be
in a write protected state, provided the VCC fall
time is not less than tF. The M48Z129Y/V may re-
spond to transient noise spikes on VCC that cross
into the deselect window during the time the de-
vice is sampling VCC. Therefore, decoupling of the
power supply lines is recommended.
When VCC drops below VSO, the control circuit
switches power to the internal battery, preserving
The internal energy source will maintain
data in the M48Z129Y/V for an accumulated peri-
od of at least 10 years at room temperature. As
system power rises above VSO, the battery is dis-
connected, and the power supply is switched to
external VCC. Deselect continues for tREC after
VCC reaches VPFD(max).
For more information on Battery Storage Life refer
to the Application Note AN1012.
All microprocessors have a reset input which forc-
es them to a known state when starting. The
M48Z129Y/V has a reset output (RST) pin which
is guaranteed to be low below VPFD(min). This sig-
nal is an open drain configuration. An appropriate
pull-up resistor should be chosen to control the
rise time. This signal will be valid for all voltage
conditions, even when VCC equals VSS. Once VCC
exceeds the power failure detect voltage VPFD, an
internal timer keeps RST low for tREC to allow the
power supply to stabilize.
The M48Z129Y/V automatically performs battery
voltage monitoring upon power-up, and at factory-
programmed time intervals of 24 hours. The Bat-
tery Low (BL) pin will be asserted if the battery volt-
age is found to be less than approximately 2.5V. If
a battery low is generated during a power-up se-
quence, this indicates that the battery is below 2.5
volts and may not be able to maintain data integrity
in the SRAM. Data should be considered suspect,
and verified as correct.
If a battery low indication is generated during the
24-hour interval check, this indicates that the bat-
tery is near end of life. However, data is not com-
promised due to the fact that a nominal VCC is
The M48Z129Y/V only monitors the battery when
a nominal VCC is applied to the device. Thus ap-
plications which require extensive durations in the
battery back-up mode should be powered-up peri-
odically (at least once every few months) in order
for this technique to be beneficial. Additionally, if
a battery low is indicated, data integrity should be
verified upon power-up via a checksum or other
technique. The BL pin is an open drain output and
an appropriate pull-up resistor should be chosen
to control the rise time.
Table 4. AC Measurement Conditions
Note that Output Hi-Z is defined as the point where data is no longer
Input Rise and Fall Times
≤ 5ns
Input Pulse Voltages
0 to 3V
Input and Output Timing Ref. Voltages
Figure 4. AC Testing Load Circuit
Note: 1. 50pF for M48Z129V (3.3V).
CL = 100pF
or 50pF
CL includes JIG capacitance

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