DS1337 I2C Serial Real-Time Clock
Table 3. Alarm Mask Bits
ALARM 1 REGISTER MASK BITS
(BIT 7)
ALARM RATE
DY/DT
A1M4
A1M3
A1M2
A1M1
X
X
X
X
1
1
1
1
1
1
1
0
1
1
0
0
1
0
0
0
Alarm once per second
Alarm when seconds match
Alarm when minutes and seconds match
Alarm when hours, minutes, and seconds match
Alarm when date, hours, minutes, and seconds
match
Alarm when day, hours, minutes, and seconds match
0
1
0
0
0
0
0
0
0
0
ALARM 2 REGISTER MASK BITS
(BIT 7)
ALARM RATE
DY/DT
A2M4
A2M3
A2M2
X
X
X
0
1
1
1
0
0
1
1
0
0
0
1
0
0
0
0
Alarm once per minute (00 seconds of every minute)
Alarm when minutes match
Alarm when hours and minutes match
Alarm when date, hours, and minutes match
Alarm when day, hours, and minutes match
1
SPECIAL-PURPOSE REGISTERS
The DS1337 has two additional registers (control and status) that control the RTC, alarms, and square-wave
output.
Control Register (0Eh)
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0
0
RS2
RS1
INTCN
A2IE
A1IE
EOSC
Bit 7: Enable Oscillator (EOSC). This active-low bit when set to logic 0 starts the oscillator. When this bit is set to
logic 1, the oscillator is stopped. This bit is enabled (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 selected with the
RS bits. These bits are both set to logic 1 (32kHz) when power is first applied.
SQW/INTB Output
A2IE
SQW/INTB
OUTPUT
INTCN
RS2
RS1
0
0
0
0
1
0
0
1
1
X
0
1
0
1
X
1Hz
X
X
X
X
1
4.096kHz
8.192kHz
32.768kHz
A2F
Bit 2: Interrupt Control (INTCN). This bit controls the relationship between the two alarms and the interrupt output
pins. When the INTCN bit is set to logic 1, a match between the timekeeping registers and the alarm 1 registers l
activates the INTA pin (provided that the alarm is enabled) and a match between the timekeeping registers and the
alarm 2 registers activates the SQW/INTB pin (provided that the alarm is enabled). When the INTCN bit is set to
logic 0, a square wave is output on the SQW/INTB pin. This bit is set to logic 0 when power is first applied.
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