M48T37 ST Microelectronics, M48T37 Datasheet - Page 13

• Manufacturer Part Number: M48T37
• Description: 3.3V-5V 256 Kbit 32Kb x8 TIMEKEEPER SRAM
• Manufacturer: ST Microelectronics

Figure 11. Interrupt Reset Waveforms
seconds per month which corresponds to a total
range of +5.5 or –2.75 minutes per month.
Two methods are available for ascertaining how
much calibration a given M48T37Y/37V may re-
quire. The first involves simply setting the clock,
letting it run for a month and comparing it to a
known accurate reference (like WWW broad-
casts). While that may seem crude, it allows the
designer to give the end user the ability to calibrate
his clock as his environment may require, even af-
ter the final product is packaged in a non-user ser-
viceable enclosure. All the designer has to do is
provide a simple utility that accesses the Calibra-
tion byte.
The second approach is better suited to a manu-
facturing environment, and involves the use of the
IRQ/FT pin. The pin will toggle at 512Hz when the
Stop bit (ST, D7 of 7FF9h) is ‘0’, the Frequency
Test Bit (FT, D6 of 7FFCh) is ‘1’, the Alarm Flag
Enable Bit (AFE, D7 of 7FF6h) is ‘0’, and the
Watchdog Steering bit (WDS, D7 of 7FF7h) is ‘1’
or the Watchdog Register is reset (7FF7h=0).
Any deviation from 512 Hz indicates the degree
and direction of oscillator frequency shift at the test
temperature. For example, 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 IRQ/FT pin is an open drain output which re-
quires a pull-up resistor for proper operation. A
500-10k
control the rise time. The FT bit is cleared on pow-
er-down.
For more information on calibration, see the Appli-
cation Note AN934 ”TIMEKEEPER Calibration”.
resistor is recommended in order to
A0-A14
ACTIVE FLAG BIT
IRQ/FT
ADDRESS 7FF0h
15ns Min
SETTING ALARM CLOCK
Registers 7FF5h-7FF2h contain the alarm set-
tings. The alarm can be configured to go off at a
predetermined time on a specific day of the month
or repeat every day, hour, minute, or second. It
can also be programmed to go off while the
M48T37Y/37V is in the battery back-up mode of
operation to serve as a system wake-up call.
RPT1-RPT4 put the alarm in the repeat mode of
operation. Table 12 shows the possible configura-
tions. Codes not listed in the table default to the
once per second mode to quickly alert the user of
an incorrect alarm setting.
Note: User must transition address (or toggle chip
enable) to see Flag bit change.
When the clock information matches the alarm
clock settings based on the match criteria defined
by RPT1-RPT4, AF is set. If AFE is also set, the
alarm condition activates the IRQ/FT pin. To dis-
able alarm, write ’0’ to the Alarm Date registers
and RPT1-4. The alarm flag and the IRQ/FT out-
put are cleared by a read to the Flags register.
The IRQ/FT pin can also be activated in the bat-
tery back-up mode. The IRQ/FT will go low if an
alarm occurs and both Alarm in Battery Back-up
Mode Enable (ABE) and AFE are set. The ABE
and AFE bits are reset during power-up, therefore
an alarm generated during power-up will only set
AF. The user can read the Flag Register at system
boot-up to determine if an alarm was generated
while the M48T37Y/37V was in the deselect mode
during power-up. Figure 12 illustrates the back-up
mode alarm timing.
AI01677B
M48T37Y, M48T37V
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