Datasheet

ADT7301
Rev. B | Page 11 of 16
SCLK
DOUT
DIN
POWER-
DOWN
LEADING ZEROS
DB13 DB0
1
2 3 4
15
16
t
1
t
2
t
3
t
4
t
6
t
5
t
7
t
8
DB12
DB1
DB0
02884-0-007
CS
Figure 14. Serial Interface Timing Diagram
SERIAL INTERFACE
The serial interface on the ADT7301 consists of four wires:
CS
, SCLK, DIN, and DOUT. The interface can be operated in
3-wire mode with DIN tied to ground, in which case the inter-
face has read-only capability, with data being read from the data
register via the DOUT line. It is advisable to always use
CS
to
create a communications window, as shown in
Figure 14; this
improves synchronization between the ADT7301 and the master
device. The DIN line is used to write the part into standby mode,
if required. The
CS
line is used to select the device when more
than one device is connected to the serial clock and data lines.
The part operates in a slave mode and requires an externally
applied serial clock to the SCLK input to access data from the
data register. The serial interface on the ADT7301 allows the
part to be interfaced to systems that provide a serial clock
synchronized to the serial data, such as the 80C51, 87C51,
68HC11, 68HC05, and PIC16Cxx microcontrollers as well as
DSP processors.
A read operation from the ADT7301 accesses data from the
temperature value register, while a write operation to the part
writes data to the control register.
Read Operation
Figure 14 shows the timing diagram for a serial read from the
ADT7301. The
CS
line enables the SCLK input. Thirteen bits of
data plus a sign bit are transferred during a read operation.
Read operations occur during streams of 16 clock pulses. The
first 2 bits out are leading zeros and the next 14 bits contain the
temperature data. If
CS
remains low and 16 more SCLK cycles
are applied, the ADT7301 loops around and outputs the two
leading zeros plus the 14 bits of data that are in the temp-
erature value register. When
CS
returns high, the DOUT line
goes into three-state. Data is clocked out onto the DOUT line
on the falling edge of SCLK.
Write Operation
Figure 14 also shows the timing diagram for a serial write to the
ADT7301. The write operation takes place at the same time as
the read operation. Only the third bit in the data stream provides
a user-controlled function. This third bit is the power-down bit,
which, when set to 1, puts the ADT7301 into shutdown mode.
In addition to the power-down bit, all bits in the input data
stream should be 0 to ensure correct operation of the ADT7301.
Data is loaded into the control register on the 16
th
rising SCLK
edge; the data takes effect at this time. Therefore, if the part is
programmed to go into shutdown, it does so at this point. If
CS
is brought high before this 16
th
SCLK edge, the control register
is not loaded and the power-down status of the part does not
change. Data is clocked into the ADT7301 on the rising edge
of SCLK.