ADT7301

Rev. B | Page 11 of 16

SCLK

DOUT

DIN

POWER-

DOWN

LEADING ZEROS

DB13

DB0

1

2

3

4

15

16

DB12

DB1

DB0

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.

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 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.