DS17285(1998) View Datasheet(PDF) - Dallas Semiconductor -> Maxim Integrated
Part Name
Description
Manufacturer
DS17285 Datasheet PDF : 32 Pages
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DS17285/DS17287
DS17285 REAL TIME CLOCK ADDRESS MAP Figure 2
0
00H
CLOCK/
CALENDAR
14 BYTES
13
0DH
14
0EH
50 BYTES
63 USER RAM 03FH
64
040H
BANK 0,
BANK 1
REGISTERS,
RAM
127
07FH
0
SECONDS
1
SECONDS ALARM
2
MINUTES
3
MINUTES ALARM
4
HOURS
5
HOURS ALARM
6
DAY OF THE WEEK
7
DAY OF THE MONTH
8
MONTH
9
YEAR
10
REGISTER A
11
REGISTER B
12
REGISTER C
13
REGISTER D
TIME, CALENDAR AND ALARM LOCATIONS
The time and calendar information is obtained by read-
ing the appropriate register bytes shown in Table 1. The
time, calendar, and alarm are set or initialized by writing
the appropriate register bytes. The contents of the time,
calendar, and alarm registers can be either Binary or
Binary–Coded Decimal (BCD) format. Table 1 shows
the binary and BCD formats of the twelve time, calendar,
and alarm locations that reside in both bank 0 and in
bank 1, plus the two extended registers that reside in
bank 1 only (bank 0 and bank 1 switching will be
explained later in this text).
Before writing the internal time, calendar, and alarm reg-
isters, the SET bit in Register B should be written to a
logic one to prevent updates from occurring while
access is being attempted. Also at this time, the data
format (binary or BCD), should be set via the data mode
bit (DM) of Register B. All time, calendar, and alarm reg-
isters must use the same data mode. The set bit in Reg-
ister B should be cleared after the data mode bit has
been written to allow the real–time clock to update the
time and calendar bytes.
Once initialized, the real–time clock makes all updates
in the selected mode. The data mode cannot be
changed without reinitializing the ten data bytes. The
24/12 bit cannot be changed without reinitializing the
hour locations. When the 12–hour format is selected,
the high order bit of the hours byte represents PM when
it is a logic one. The time, calendar, and alarm bytes are
always accessible because they are double buffered.
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 four 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 inter-
rupt 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 four 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 gener-
ated 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. The
three alarm bytes may be used in conjunction with the
date alarm as described in the Wakeup/Kickstart sec-
tion. The century counter will be discussed later in this
text.
030598 6/32
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