Preliminary Technical Data

ADT7302

Rev. PrE | Page 9 of 14

SCLK

DOUT

DIN

POWER-

DOWN

LEADING ZEROS

DB13

12

3

4

15

16

DB12

DB1

DB0

CS

Figure 13. Serial Interface Timing Diagram

SERIAL INTERFACE

The serial interface on the ADT7302 consists of four wires: CS,

SCLK, DIN, and DOUT. The interface can be operated in 2-

wire mode with CS and 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 utilize CS,

which improves synchronization between the ADT7302 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 ADT7302 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 ADT7302 accesses data from the

temperature value register while a write operation to the part

writes data to the control register.

Read Operation

Figure 13 shows the timing diagram for a serial read from the

ADT7302. 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 two 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 ADT7302 loops around and outputs the

two leading zeros plus the 14 bits of data that are in the temper-

ature 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 13 also shows the timing diagram for a serial write to the

ADT7302. 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 a 1, puts the ADT7302 into

shutdown mode. Besides the power-down bit, all bits in the

input data stream should be zero to ensure correct operation of

the ADT7302. Data is loaded into the control register on the

16

the part is programmed to go into shutdown, it does so at this

point. If CS is brought high before this 16

control register is not loaded and the power-down status of the

part does not change. Data is clocked into the ADT7302 on the

rising edge of SCLK.