ADT7301

Rev. B | Page 12 of 16

APPLICATIONS INFORMATION

MICROPROCESSOR INTERFACING

The ADT7301 serial interface allows easy interface to most

microcomputers and microprocessors. Figure 15 to Figure 18

show some typical interface circuits. The serial interface on the

ADT7301 consists of four wires: CS, DIN, DOUT, and SCLK.

All interface circuits shown use all four interface lines. However,

it is possible to operate the interface with three wires. If the

application does not require the power-down facility offered

by the ADT7301, the DIN line can be tied low permanently.

Thus, the interface can be operated from just three wires: SCLK,

CS, and DOUT.

The serial data transfer to and from the ADT7301 requires a

16-bit read operation. Many 8-bit microcontrollers have 8-bit

serial ports, and this 16-bit data transfer is handled as two 8-bit

transfers. Other microcontrollers and DSP processors transfer

16 bits of data in a serial data operation.

ADT7301-to-MC68HC11 Interface

Figure 15 shows an interface circuit between the ADT7301 and

the MC68HC11 microcontroller. The MC68HC11 is configured

in master mode with its CPOL and CPHA bits set to a Logic 1.

When the MC68HC11 is configured like this, its SCLK line idles

high between data transfers. Data is transferred to and from the

ADT7301 in two 8-bit serial data operations. Figure 15 shows

the full (4-wire) interface. PC1 of the MC68HC11 is configured

as an output and is used to drive the CS input.

ADT7301*

SCLK

DOUT

DIN

MC68HC11*

SCLK

MISO

MOSI

PC1

*ADDITIONAL PINS OMITTED FOR CLARITY

CS

Figure 15. ADT7301-to-MC68HC11 Interface

ADT7301-to-8051 Interface

Figure 16 shows an interface circuit between the ADT7301 and

the microcontroller. The 8051 is configured in its Mode 0 serial

interface mode. The serial clock line of the 8051 (on P3.1) idles

high between data transfers. Data is transferred to and from the

ADT7301 in two 8-bit serial data operations. The ADT7301

outputs the MSB of its data stream as the first valid bit while the

8051 expects the LSB first. Thus, the data read into the serial

buffer needs to be rearranged before the correct data-word from

the ADT7301 is available in the accumulator.

In the example shown in Figure 16, the ADT7301 is connected

to the serial port of the 8051. Because the serial interface of the

8051 contains only one data line, the DIN line of the ADT7301

is tied low in Figure 16.

For applications that require the ADT7301 power-down feature,

the serial interface should be implemented using data port lines

on the 8051. This allows a full-duplex serial interface to be

implemented. The method involves generating a serial clock on

one port line while using two other port lines to shift data

in and out with the fourth port line connecting to CS. Port

lines 1.0 to 1.3 (with P1.1 configured as an input) can be used

to connect to SCLK, DOUT, DIN, and CS, respectively, to

implement this scheme.

ADT7301*

SCLK

DOUT

DIN

8051*

P3.1

P3.0

P1.2

P1.3

*ADDITIONAL PINS OMITTED FOR CLARITY

CS

Figure 16. ADT7301-to-8051 Interface

ADT7301-to-PIC16C6x/7x Interface

Figure 17 shows an interface circuit between the ADT7301 and

the PIC16C6x/7x microcontroller. The PIC16C6x/7x synchro-

nous serial port (SSP) is configured as an SPI master with the

clock polarity bit set to a Logic 1. In this mode, the serial clock

line of the PIC16C6x/7x idles high between data transfers. Data

is transferred to and from the ADT7301 in two 8-bit serial data

operations. In the example shown in Figure 17, port line RA1 is

being used to generate the CS for the ADT7301.

ADT7301*

SCLK

DOUT

DIN

PIC16C6x/7x*

SCK

SDO

SDI

RA1

*ADDITIONAL PINS OMITTED FOR CLARITY

CS

Figure 17. ADT7301-to-PIC16C6x/7x Interface