PT7C4372A Datasheet, PDF (6/30 Pages) Pericom Semiconductor Corporation – Real-time Clock Module

PT7C4372A/4372C
Real-time Clock Module (I²C Bus)
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Function Description
Overview of Functions
Clock function
CPU can read or write data including the year (last two
digits), month, date, day, hour, minute, and second. Any
(two-digit) year that is a multiple of 4 is treated as a leap
year and calculated automatically as such until the year 2099.
Clock precision adjustment function
They have two internal oscillation circuit capacitors, so that
an oscillation circuit may be configured simply by
externally connecting a crystal. Either 32.768kHz or
32.000kHz crystal may be selected to setting the internal
register appropriately.
The clock precision can be adjusted forward or back in units
of ±3.051 ppm (32.768kHz crystal) or ±3.125 ppm
(32.000kHz crystal) and oscillation frequency can be
adjusted in ±189 ppm (32.768kHz crystal) or ±194 ppm
(32.000kHz crystal).
This function can be used to implement a higher-precision
clock function, such as by:
 Enabling higher clock precision throughout the year by
taking seasonal clock precision adjustments into
account in advance, or
 Enabling correction of temperature-related clock
precision variation in systems that include a
temperature detecting function.
Periodic interrupt
 PT7C4372A/C
Periodic interrupts can be output via the /INTA and /INTB
pins.
Select among five Periodic frequency settings: 2 Hz (every
0.5 seconds), 1 Hz (every second), 1/60 Hz (every minute),
1/3600Hz (every hour), or monthly.
Select among two output waveforms for periodic interrupts:
ordinary pulse waveform (2 Hz or 1 Hz) or waveforms
(every second, minute, hour, or month) for CPU-level
interrupts that can support CPU interrupts.
A polling function is also provided to enable monitoring of
pin states via registers.
Alarm function
 PT7C4372A/C
This module is has two alarm system (Alarm_A and
Alarm_B) that outputs interrupt signals from /INTA or
/INTB to CPU when the day of the week, hour or minute
corresponds to the setting. Each of them may output
interrupt signal separately at a specified time. The alarm
may be selectable between on and off for each day of the
week, thus allowing outputting alarm everyday or on a
specific day of the week.
The Alarm_A is output from the /INTA pin while the
Alarm_B is output from either the /INTA or the /INTB pins.
Polling is possible separately for each alarm function.
Oscillation stop detection function, power drop detection
function (voltage monitoring function), and power-on
reset detection function
PT7C4372A/ C have only oscillation stop detection function.
The oscillation stop detection function uses registers to
record if clock data is valid or invalid. This function may be
used to determine if the PT7C4372A/C supply power has
been booted from 0V and if it has been backed up.
Interface with CPU
Data is read and written via the I²C bus interface using two
signal lines: SCL (clock) and SDA (data).
Since the output of the I/O pin of SDA is open drain, a pull-
up resistor should be used on the circuit board if the CPU
output I/O is also open drain.
The SCL's maximum clock frequency is 400 kHz, which
supports the I²C bus's high-speed mode.
32-kHz clock output
The 32.768 kHz clock (32.768kHz crystal) or 32.000kHz
clock (32.000kHz crystal) can be output via the /INTB by
setting corresponding register.
Note: The precision of this 32.768 kHz clock output via the
FOUT pin can not be adjusted (even when using the clock
precision adjustment function).
12-07-0001
PT0150-8 07/04/12
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