M48T37V-10MH1F STMicroelectronics, M48T37V-10MH1F Datasheet - Page 16

• Manufacturer Part Number: M48T37V-10MH1F
• Description: IC TIMEKPR NVRAM 256KB 3V 44-SOH
• Manufacturer: STMicroelectronics
• Series: Timekeeper®r
• Type: Clock/Calendar/NVSRAMr

Specifications of M48T37V-10MH1F

• Memory Size: 256K (32K x 8)
• Time Format: HH:MM:SS (24 hr)
• Date Format: YY-MM-DD-dd
• Interface: Parallel
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 44-SOH
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-4718-2

Clock operations
Note:
3.6
Note:
Note:
16/30
Two methods are available for ascertaining how much calibration a given M48T37Y/V may
require. The first involves simply setting the clock, letting it run for a month and comparing it
to a known accurate reference (like WWW broadcasts). 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 after the final product is packaged in a non-user serviceable enclosure.
All the designer has to do is provide a simple utility that accesses the calibration byte.
The second approach is better suited to a manufacturing environment, and involves the use
of the IRQ/FT pin. The pin will toggle at 512 Hz 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.
Setting or changing the calibration byte does not affect the frequency test output frequency.
The IRQ/FT pin is an open drain output which requires a pull-up resistor for proper
operation. A 500-10 kΩ resistor is recommended in order to control the rise time. The FT bit
is cleared on power-down.
For more information on calibration, see the application note AN934, “TIMEKEEPER
calibration.”
Watchdog timer
The watchdog timer can be used to detect an out-of-control microprocessor. The user
programs the watchdog timer by setting the desired amount of time-out into the eight-bit
watchdog register, address 7FF7h. The five bits (BMB4-BMB0) that store a binary multiplier
and the two lower order bits (RB1-RB0) select the resolution, where 00 =
01 =
determined to be the multiplication of the five-bit multiplier value with the resolution. (For
example: writing 00001110 in the watchdog register = 3x1, or 3 seconds).
Accuracy of timer is within ± the selected resolution.
If the processor does not reset the timer within the specified period, the M48T37Y/V sets the
watchdog flag (WDF) and generates a watchdog interrupt or a microprocessor reset. WDF
is reset by reading the flags register (Address 7FF0h).
User must transition address (or toggle chip enable) to see flag bit change.
Reset will not occur unless the addresses are stable at the flag location for at least 15 ns
while the device is in the READ mode as shown in
The most significant bit of the watchdog register is the watchdog steering bit. When set to a
'0,' the watchdog will activate the IRQ/FT pin when timed-out. When WDS is set to a '1,' the
watchdog will output a negative pulse on the RST pin for a duration of t
register, the FT bit, AFE bit, and ABE bit will reset to a '0' at the end of a watchdog time-out
when the WDS bit is set to a '1.'
The watchdog timer resets when the microprocessor performs a re-write of the watchdog
register or an edge transition (low to high / high to low) on the WDI pin occurs. The timeout
period then starts over.
1
/
4
second, 10 = 1 second, and 11 = 4 seconds. The amount of time-out is then
Doc ID 7019 Rev 9
Figure 9 on page
19.
M48T37Y, M48T37V
REC
1
/
. The watchdog
16
second,