ADT7302_05 Datasheet, PDF (12/16 Pages) Analog Devices – ±2 C Accurate, Micropower Digital Temperature Sensor

ADT7302
APPLICATIONS
MICROPROCESSOR INTERFACING
The ADT7302’s serial interface allows easy interface to most
microcomputers and microprocessors. Figure 15 through
Figure 18 show some typical interface circuits. The serial
interface on the ADT7302 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 ADT7302, 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 ADT7302 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.
ADT7302 to MC68HC11 Interface
Figure 15 shows an interface between the ADT7302 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 ADT7302 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.
ADT7302*
SCLK
DOUT
DIN
CS
MC68HC11*
SCLK
MISO
MOSI
PC1
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 15. ADT7302 to MC68HC11 Interface
ADT7302 to 8051 Interface
Figure 16 shows an interface circuit between the ADT7302 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
ADT7302 in two 8-bit serial data operations. The ADT7302
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 ADT7302 is available in the accumulator.
In the example, the ADT7302 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 ADT7302 is tied low in
Figure 16.
For applications that require the ADT7302 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 “bit-banging” a port line to
generate a serial clock while using two other port lines to shift
data in and out with the fourth port line connecting to CS. Port
lines 1.0 through 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.
ADT7302*
SCLK
DOUT
DIN
CS
8051*
P1.1
P1.0
P1.2
P1.3
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 16. ADT7302 to 8051 Interface
ADT7302 to PIC16C6x/7x and PIC16F873 Interface
Figure 17 shows an interface circuit between the ADT7302 and
the PIC16C6x/7x microcontroller. The PIC16C6x/7x
synchronous 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 ADT7302 in two
8-bit serial data operations. In the example shown, port line
RA1 is being used to generate the CS for the ADT7302.
ADT7302*
SCLK
DOUT
DIN
CS
PIC16C6x/7x*
SCLK
SDO
SDI
RA1
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 17. ADT7302 to PIC16C6x/7x Interface
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