DS1685 Maxim, DS1685 Datasheet - Page 5

• 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

PIN DESCRIPTIONS (continued)
TSSOP
PDIP,
SO,
18
19
20
21
22
23
24
DS1685
PLCC
PIN
22
23
24
25
26
27
28
DS1687
EDIP
18
19
21
22
23
24
—
NAME
RCLR
V
SQW
V
IRQ
V
KS
BAUX
BAT
CC
Kickstart Input, Active Low. When V
DS1685/DS1687, the system can be powered on in response to an active-
low transition on the KS pin, as might be generated from a key closure.
V
start enable bit (KSE) must be set to 1 if the kickstart function is used, and
the KS pin must be pulled up to the V
KS pin can be used as an interrupt input. If not used, connect to V
V
Interrupt-Request Output, Open Drain, Active Low. The IRQ pin is an
active-low output of the DS1685/DS1687 that can be connected to the
interrupt input of a processor. The IRQ output remains low as long as the
status bit causing the interrupt is present and the corresponding interrupt-
enable bit is set. To clear the IRQ pin, the application software must clear
all the enabled flag bits contributing to IRQ’s active state asserted but
without asserting CS latch addresses. However, no data transfer occurs.
Battery Input for Any Standard 3V Lithium Cell or Other Energy Source.
Battery voltage must be held between 2.5V and 3.7V for proper operation.
V
V
RAM Clear Input, Active Low. If enabled by software, taking RCLR low
clears the 242 bytes of user RAM to FFh. When enabled, RCLR can be
activated whether or not V
be used by a human interface (shorting to ground manually or by a switch)
and not to be driven with external buffers. This pin is internally pulled up.
Do not use an external pullup resistor on this pin.
Auxiliary Battery Input. Required for kickstart and wake-up features. This
input also supports clock/ calendar and user RAM if V
or is not present. A standard +3V lithium cell or other energy source can be
used. Battery voltage must be held between +2.5V and +3.7V for proper
operation. If V
Auxiliary-Battery Enable bit bank 1, register 4BH, should be written to 0.
See “Conditions of Acceptability” at www.maxim-ic.com/UL.
Square-Wave Output. The SQW pin provides a 32kHz square-wave output,
t
following bits, enabling the 32kHz output; DV1 = 1, and E32K = 1. A square
wave is output on this pin if either SQWE = 1 or E32K = 1. If E32K = 1, then
32kHz is output regardless of the other control bits. If E32K = 0, then the
output frequency is dependent on the control bits in register A. The SQW
pin can output a signal from one of 13 taps provided by the 15 internal
divider stages of the RTC. The frequency of the SQW pin can be changed
by programming Register A as shown in Table 3. The SQW signal can be
turned on and off using the SQWE bit in register B or the E32K bit in
extended register 4Bh. A 32kHz SQW signal is output when the enable-
32kHz (E32K) bit in extended register 4Bh is a logic 1 and V
V
E32K = 1, ABE = 1, and voltage is applied to the V
DC Power for Primary Power Supply. When V
normal limits, the device sis fully accessible and data can be written and
read. When V
www.maxim-ic.com/UL.
REC
BAUX
BAUX
BAT
BAT
PF
. A 32kHz square wave is also available when V
, after a power-up condition has been detected. This condition sets the
must be grounded if not used. Diodes should not be placed between
and the battery. See “Conditions of Acceptability” at
must be present and the auxiliary-battery enable bit (ABE) and kick-
if V
5 of 34
BAUX
CC
BAUX
is used.
is below V
is not going to be used it should be grounded, and
CC
PF
DS1685/DS1687 3V/5V Real-Time Clocks
is present. The RCLR function is designed to
reads and writes are inhibited.
FUNCTION
CC
BAUX
is removed from the
supply. While V
CC
is applied within the
BAUX
CC
BAT
is less than V
pin.
is at lower voltage
CC
CC
is applied, the
is above
CC
PF
, or to
if