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VT82887 Datasheet(PDF) 6 Page - List of Unclassifed Manufacturers

Part No. VT82887
Description  Real Time Clock
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Maker  ETC1 [List of Unclassifed Manufacturers]
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VT82887 Datasheet(HTML) 6 Page - List of Unclassifed Manufacturers

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VT82887
Real Time Clock
VIA Technologies, Inc.
represents PM when it is a logic one. Once
per second the ten bytes are advanced by
one second and checked for an alarm
condition. If a read of the time and calendar
data occurs during an update, a problem
exists where seconds, minutes, hours, etc.
may not correlate. The probability of reading
incorrect time and calendar data is low.
Several methods of avoiding any possible
incorrect
time
and
calendar
reads
are
covered later in this text.
The three alarm bytes can be used in two
ways. First, when the alarm time is written in
the appropriate hours, minutes and seconds
alarm locations, the alarm interrupt is initiated
at the specified time each day if the alarm
enable bit is high. The second use condition
is to insert a “don’t care” state in one or more
of the three alarm bytes. The “don’t care”
code is any hexadecimal value from C0 to FF.
The two most significant bits of each byte set
the “don’t care” condition when at logic 1. An
alarm will be generated each hour when the
“don’t care” bits are set in the hours byte.
Similarly, an alarm is generated every minute
with “don’t care” codes in the hours and
minute alarm bytes. The “don’t care” codes
in all three alarm bytes create an interrupt
every second.
TABLE 2: TIME. CALENDAR AND ALARM DATA MODES
ADDRESS
DECIMAL
RANGE
LOCATION
FUNCTION
RANGE
BINARY DATA MODE
BCD DATA MODE
0
Seconds
0-59
00-3B
00-59
1
Seconds Alarm
0-59
00-3B
00-59
2
Minutes
0-59
00-3B
00-59
3
Minutes Alarm
0-59
00-3B
00-59
4
Hours-12-hr Mode
1-12
01-0C AM, 81-8C PM
01-12AM,81-92PM
Hours-24-hr Mode
0-23
00-17
00-23
5
Hours Alarm-12-hr
1-12
01-0C AM, 81-8C PM
01-12AM,81-92PM
Hours Alarm-24-hr
0-23
00-17
00-23
6
Day of the Week
Sunday = 1
1-7
01-07
01-07
7
Date of the Month
1-31
01-1F
01-31
8
Month
1-12
01-0C
01-12
9
Year
0-99
00-63
00-99
NONVOLATILE RAM
The 114 general purpose nonvolatile RAM
bytes are not dedicated to any special
function within the VT82887. They can be
used by the processor program as nonvolatile
memory and are fully available during the
update cycle.
INTERRUPTS
The RTC plus RAM includes three separate,
fully automatic sources of interrupt for a
processor.
The
alarm
interrupt
can
be
programmed to occur at rates from once per
second to once per day. The periodic interrupt
can be selected for rates from 500 ms to 122
µs. The update-ended interrupt can be used
to indicate to the program that an update
cycle is complete. Each of these independent


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