DS1390/DS1391/DS1392/DS1393
Bit 7: Enable Oscillator (EOSC). When set to logic 0,
this bit starts the oscillator. When this bit is set to logic
1, the oscillator is stopped whenever the device is pow-
ered by V
BACKUP
. The oscillator is always enabled
when V
CC
is valid. This bit is enabled (logic 0) when
V
CC
is first applied.
Bit 5: Battery-Backed Square-Wave and Interrupt
Enable (BBSQI). This bit when set to logic 1 enables
the square wave or interrupt output when V
CC
is absent
and the DS1390/DS1392/DS1393 are being powered
by the V
BACKUP
pin. When BBSQI is logic 0, the
SQW/INT pin (or SQW and INT pins) goes high imped-
ance when V
CC
falls below the power-fail trip point.
This bit is disabled (logic 0) when power is first applied.
Bits 4 and 3: Rate Select (RS2 and RS1). These bits
control the frequency of the square-wave output when
the square wave has been enabled. The table below
shows the square-wave frequencies that can be select-
ed with the RS bits. These bits are both set to logic 1
(32kHz) when power is first applied.
Bit 2: Interrupt Control (INTCN). This bit controls the
SQW/INT signal. When the INTCN bit is set to logic 0, a
square wave is output on the SQW/INT pin. The oscilla-
tor must also be enabled for the square wave to be out-
put. When the INTCN bit is set to logic 1, a match
between the timekeeping registers and either of the
alarm registers then activates the SQW/INT (provided
the alarm is also enabled). The corresponding alarm
flag is always set, regardless of the state of the INTCN
bit. The INTCN bit is set to logic 0 when power is first
applied.
Bit 0: Alarm Interrupt Enable (AIE). When set to logic
1, this bit permits the alarm flag (AF) bit in the status
register to assert SQW/INT (when INTCN = 1). When
the AIE bit is set to logic 0 or INTCN is set to logic 0,
the AF bit does not initiate the SQW/INT signal. The AIE
bit is disabled (logic 0) when power is first applied.
Low-Voltage SPI/3-Wire RTCs with
Trickle Charger
16 ____________________________________________________________________
Special-Purpose Registers
The DS1390–DS1393 have three additional registers
(control, status, and trickle charger) that control the
RTC, alarms, square-wave output, and trickle charger.
Control bits used in the DS1390 become general-pur-
pose, battery-backed, nonvolatile SRAM bits in the
DS1391.
(8 paginas)
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