DS1391 Maxim, DS1391 Datasheet - Page 12

• Manufacturer Part Number: DS1391
• Description: The low-voltage serial-peripheral interface (SPI™) DS1390/DS1391/DS1394 and the low-voltage 3-wire DS1392/DS1393 real-time clocks (RTCs) are clocks/calendars that provide hundredths of a second, seconds, minutes, hours, day, date, month, and ye
• Manufacturer: Maxim

Low-Voltage SPI/3-Wire RTCs with
Trickle Charger
The DS1390–DS1394 RTCs are low-power clocks/calen-
dars with alarms. Address and data are transferred seri-
ally through a 4-wire SPI interface for the DS1390 and
DS1391 and through a 3-wire interface for the DS1392,
DS1393, and DS1394. The DS1390/DS1391 operate as a
slave device on the SPI serial bus. The DS1392/DS1393
operate using a 3-wire synchronous serial bus. Access is
obtained by selecting the part by the CS pin (CE on
DS1392/DS1393) and clocking data into/out of the part
using the SCLK and DIN/DOUT pins (I/O on
DS1392/DS1393). Multiple-byte transfers are supported
within one CS low period (see the SPI Serial-Data Bus
12
(DS1390/91/94) DOUT
(DS1390/91/94) DIN
(DS1390/91/94) CS
(DS1392/93) (CE)
(DS1392/93) I/O
____________________________________________________________________
V
BACKUP
SCLK
GND
V
X1
X2
CC
Detailed Description
V
TRICKLE CHARGER
CC
POWER SWITCH,
WRITE PROTECT,
INTERFACE
LEVEL DETECT,
C
C
BUS
L
L
WITH HUNDREDTHS
REAL-TIME CLOCK
ALARM REGISTERS
TRICKLE REGISTER
CONTROL/STATUS
HUNDREDTHS-OF-
OF SECONDS
REGISTERS
GENERATOR
SECONDS
section). The clocks/calendars provide hundredths of
seconds, seconds, minutes, hours, day, date, month,
and year information. The alarm functions are performed
off all timekeeping registers, allowing the user to set high
resolution alarms. The date at the end of the month is
automatically adjusted for months with fewer than 31
days, including corrections for leap year. The clocks
operate in either the 24-hour or 12-hour format with an
AM/PM indicator. All five devices have a built-in tempera-
ture-compensated voltage reference that detects power
failures and automatically switches to the battery supply.
Additionally, the devices can provide trickle charging of
the backup voltage source, with selectable charging
resistance and diode voltage drops.
SELECTOR, INT, MUX,
SQUARE-WAVE RATE
DS1392/DS1393/DS1394
RST OUTPUT
DS1390/DS1391/
Functional Diagram
N
SQW/INT (DS1390/93/94)
RST (DS1391)
SQW (DS1392)