DS1375 Datasheet, PDF (10/13 Pages) Dallas Semiconductor – 2-Wire Digital Input RTC with Alarm

I²C Digital Input RTC with Alarm
Status Register (0Fh)
Bit 7
0
Bit 6
0
Bit 5
0
Bit 4
0
Bit 3
0
Bit 2
0
Bit 1
A2F
Bit 0
A1F
Status Register (0Fh)
Bit 1/Alarm 2 Flag (A2F). A logic 1 in the alarm 2 flag
bit indicates that the time matched the alarm 2 regis-
ters. If the A2IE bit is logic 1 and the INTCN bit is set to
logic 1, the SQW/INT pin is also asserted. A2F is
cleared when written to logic 0. This bit can only be
written to logic 0. Attempting to write to logic 1 leaves
the value unchanged.
Bit 0/Alarm 1 Flag (A1F). A logic 1 in the alarm 1 flag
bit indicates that the time matched the alarm 1 regis-
ters. If the A1IE bit is logic 1 and the INTCN bit is set to
logic 1, the SQW/INT pin is also asserted. A1F is
cleared when written to logic 0. This bit can only be
written to logic 0. Attempting to write to logic 1 leaves
the value unchanged.
I²C Serial Data Bus
The DS1375 supports a bidirectional I²C bus and data
transmission protocol. A device that sends data onto
the bus is defined as a transmitter and a device receiv-
ing data as a receiver. The device that controls the
message is called a master. The devices that are con-
trolled by the master are slaves. A master device that
generates the serial clock (SCL), controls the bus
access, and generates the START and STOP condi-
tions must control the bus. The DS1375 operates as a
slave on the I²C bus. Connections to the bus are made
through the open-drain I/O lines SDA and SCL. Within
the bus specifications a standard mode (100kHz max
clock rate) and a fast mode (400kHz max clock rate)
are defined. The DS1375 works in both modes.
The following bus protocol has been defined (Figure 3):
• Data transfer can be initiated only when the bus is
not busy.
• During data transfer, the data line must remain
stable whenever the clock line is high. Changes in
the data line while the clock line is high can be
interpreted as control signals.
Accordingly, the following bus conditions have been
defined:
Bus not busy: Both data and clock lines remain
high.
Start data transfer: A change in the data line’s
state from high to low, while the clock line is high,
defines a START condition.
Stop data transfer: A change in the data line’s
state from low to high, while the clock line is high,
defines a STOP condition.
Data valid: The data line’s state represents valid
data when, after a START condition, the data line is
stable for the duration of the high period of the
clock signal. The data on the line must be changed
MSB FIRST
SDA
MSB
LSB
MSB
LSB
SLAVE
ADDRESS
R/W ACK
DATA
ACK
DATA
ACK/
NACK
SCL
1–7
8
9
1–7
8
9
1–7
IDLE START
CONDITION
REPEATED IF MORE BYTES
ARE TRANSFERRED
Figure 3. I²C Data Transfer Overview
10 ____________________________________________________________________
8
9
STOP CONDITION
REPEATED START