
REV. B
AD7814
–7–
In the example shown, the AD7814 is connected to the serial
port of the 8051. Because the serial interface of the 8xC51 con-
tains only one data line, the DIN line of the AD7814 is tied low
in the interface example given in Figure 4.
For applications that require the use of the power-down feature
of the AD7814, 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 config-
ured as an input) can be used to connect to SCLK, DOUT,
DIN and
CS,
respectively, to implement this scheme.
AD7814*
SCLK
DOUT
DIN
CS
8051*
P3.1
P3.0
P1.2
P1.3
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 4. AD7814 to 8051 Interface
AD7814 to PIC16C6x/7x Interface
Figure 5 shows an interface circuit between the AD7814 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 one. In this mode, the serial clock line
of the PIC16C6x/7x idles high between data transfers. Data is
transferred to and from the AD7814 in two 8-bit serial data
operations. In the example shown, port line RA1 is being used
to generate the
CS
for the AD7814.
AD7814*
SCLK
DOUT
DIN
CS
PIC16C6x/7x*
SCK
SDO
SDI
RA1
*ADDITIONAL PINS OMITTED FOR CLARITY
Figure 5. AD7814 to PIC16C6x/7x Interface
AD7814 to ADSP-21xx Interface
Figure 6 shows an interface between the AD7814 and the
ADSP-21xx DSP processor. To ensure correct operation of the
interface the SPORT Control Register should be set up as
follows:
TFSW = RFSW = 1, Alternate Framing
INVRFS = INVTFS = 1, Active Low Framing Signal
DTYPE = 00, Right Justify Data
SLEN = 1111, 16-Bit Data Words
ISCLK = 1, Internal Serial Clock
TFSR = RFS = 1, Frame Every Word
IRFS = 0, RFS Configured As Input
ITFS = 1, TFS Configured As Output
The interface requires an inverter between the SCLK line of the
ADSP-21xx and the SCLK input of the AD7814. The ADSP-
21xx has the TFS and RFS of the SPORT tied together with
TFS set as an output and RFS set as an input. The DSP operates
in Alternate Framing Mode and the SPORT Control Register is
set up as described above.
AD7814*
SCLK
DOUT
DIN
CS
ADSP-21xx*
SCK
DR
DT
RFS
*ADDITIONAL PINS OMITTED FOR CLARITY
TFS
Figure 6. AD7814 to ADSP-21xx Interface
MOUNTING THE AD7814
The AD7814 can be used for surface or air-temperature sensing
applications. If the device is cemented to a surface with ther-
mally conductive adhesive, the die temperature will be within
about 0.1
°
C of the surface temperature, thanks to the device’s
low power consumption. Care should be taken to insulate the
back and leads of the device from the air, if the ambient air
temperature is different from the surface temperature being
measured.
The ground pin provides the best thermal path to the die, so the
temperature of the die will be close to that of the printed circuit
ground track. Care should be taken to ensure that this is in good
thermal contact with the surface being measured.
As with any IC, the AD7814 and its associated wiring and cir-
cuits must be kept free from moisture to prevent leakage and
corrosion, particularly in cold conditions where condensation is
more likely to occur. Water-resistant varnishes and conformal
coatings can be used for protection. The small size of the
AD7814 package allows it to be mounted inside sealed metal
probes, which provide a safe environment for the device.
SUPPLY DECOUPLING
The AD7814 should be decoupled with a 0.1
μ
F ceramic
capacitor between V
DD
and GND. This is particularly important
if the AD7814 is mounted remote from the power supply.
TEMPERATURE – C
–0.4
–55
T
–0.2
0
0.2
0.4
0.6
0.8
1
–40
0
25
40
85
100
120
Figure 7. Typical AD7814 Temperature Error