
DS17285/DS17287/DS17485/DS17487/DS17885/DS17887
Real-Time Clocks
10
____________________________________________________________________
X1
OSCILLATOR
POWER
CONTROL
X2
DS17x87
ONLY
VBAT
GND
DIVIDE
BY 8
REGISTERS A, B, C, D
CLOCK/CALENDAR
UPDATE LOGIC
EXTENDED
USER RAM
2k/4k/8k
BYTES
SELECT
EXTENDED RAM ADDR/
DATA REGISTERS
EXTENDED CONTROL/
STATUS REGISTERS
64-BIT SERIAL NUMBER
CENTURY COUNTER
DATE ALARM
RTC ADDRESS-2
RTC ADDRESS-3
DIVIDE BY
64
DIVIDE BY
64
16:1 MUX
SQUARE-
WAVE
GENERATOR
SQW
IRQ
PWR
KS
RLCR
IRQ
GENERATOR
VCC
VBAUX
BUS
INTERFACE
CS
WR
RD
ALE
AD0–AD7
CLOCK/CALENDAR AND
ALARM REGISTERS
BUFFERED CLOCK/
CALENDAR AND ALARM
REGISTERS
USER RAM
114 BYTES
RAM
CLEAR
LOGIC
DS17x85/87
Figure 1. Functional Diagram