DS1685 Maxim, DS1685 Datasheet - Page 6

• Manufacturer Part Number: DS1685
• Description: The DS1685/DS1687 are real-time clocks (RTCs) designed as successors to the industry-standard DS1285,DS1385, DS1485, and DS1585 PC RTCs
• Manufacturer: Maxim

Figure 1. Block Diagram
OSCILLATOR CIRCUIT
The DS1685 uses an external 32.768kHz crystal. The oscillator circuit does not require any external resistors or
capacitors to operate. Table 1 specifies several crystal parameters for the external crystal, and Figure 2 shows a
functional schematic of the oscillator circuit. The oscillator is controlled by an enable bit in the control register.
Oscillator startup times are highly dependent upon crystal characteristics, PC board leakage, and layout. High ESR
and excessive capacitive loads are the major contributors to long startup times. A circuit using a crystal with the
recommended characteristics and proper layout usually starts within one second.
AD0 - AD7
DS1687 only
DS1687 only
V
GND
V
ALE
BAUX
V
W R
R D
C S
BAT
CC
X1
X2
Interface
Control
Power
OSC
BUS
DS1685/DS1687
Clock/Calender
Update Logic
Divide
by 8
6 of 34
Divide by
64
16:1 M ux
Extended RAM Addr/
64-Bit Serial Num ber
Calendar and Alarm
Clock/Calendar and
Registers A, B,C,D
User Ram
114 Bytes
Extended Control/
Status Registers
Century Counter
Alarm Registers
RTC Address -2
RTC Address -3
Buffered Clock/
Data Registers
Date Alarm
DS1685/DS1687 3V/5V Real-Time Clocks
Registers
Select
Generator
Generator
Square
W ave
Divide by
IRQ
Logic
Clear
RAM
64
R L C R
User RAM
128 Bytes
Extended
SQW
IR Q
P W R
K S