AD8802/AD8804

REV. 0

–13–

*

LDAA

$0000

Hi-byte data loaded from memory

STAA

SDI1

SDI1 = data in location 0000H

*

* Enter Contents of SDI2 Data Register

*

LDAA

$0001

Low-byte data loaded from memory

STAA

SDI2

SDI2 = Data in location 0001H

*

LDX

#SDI1

Stack pointer at 1st byte to send via SDI

LDY

#$1000

Stack pointer at on-chip registers

*

* Reset AD8802 to one-half scale (AD8804 does not have a Reset input)

*

BCLR

PORTC,Y $02

Assert /RS

BSET

PORTC,Y $02

De-Assert /RS

*

* Get AD8802/04 ready for data input

*

BCLR

PORTD,Y $02

Assert /CS

*

TFRLP

LDAA

0,X

Get a byte to transfer for SPI

STAA

SPDR

Write SDI data reg to start xfer

*

WAIT

LDAA

SPSR

Loop to wait for SPIF

BPL

WAIT

SPIF is the MSB of SPSR

*

INX

Increment counter to next byte for xfer

CPX

#SDI2+1

Are we done yet ?

BNE

TFRLP

If not, xfer the second byte

*

* Update AD8802 output

*

BSET

PORTD,Y $20

Latch register & update AD8802

*

PULA

When done, restore registers X, Y & A

PULY

PULX

RTS

** Return to Main Program **

Listing 3. AD8802/AD8804 to MC68HC11 Interface Program Source Code

An Intelligent Temperature Control System—Interfacing the

8051

C with the AD8802/AD8804 and TMP14

Connecting the 80CL51

µC, or any modern microcontroller,

with the TMP14 and AD8802/AD8804 yields a powerful tem-

perature control tool, as shown in Figure 27. For example, the

80CL51

µC controls the TrimDACs allowing the user to auto-

matically set the temperature setpoints voltages of the TMP14

via computer or touch pad, while the TMP14 senses the tem-

perature and outputs four open-collector trip-points. Feeding

these trip-point outputs back to the 80CL51

µC allow it to sense

whether or not a setpoint has been exceeded. Additional

80CL51

µC port pins or TMP14 trip-point outputs may then

be used to change fan speed (i.e., high, medium, low, off), or

increase/decrease the power level to a heater. (Please refer to the

TMP14 data sheet for more applications information.)

The CS (Chip Select) on the AD8802/AD8804 makes applica-

tions that call for large temperature sensor arrays possible. In

addition, the 12 channels of the AD8802/AD8804 allow inde-

pendent setpoint control for all four trip-point outputs on up to

three TMP14 temperature sensors. For example, assume that

the 80CL51

µC has eight free port pins available after all user

interface lines, interrupts, and the serial port lines have been

assigned. The eight port pins may be used as chip selects, in

which case an array of eight AD8802/AD8804s controlling

twenty-four TMP14 sensors is possible.

The AD8802/AD8804 and TMP14 are also ideal choices for

low power applications. These devices have power shutdown

modes and operate on a single 5 Volt supply. When their shut-

down modes are activated current consumption is reduced to

less than 35

µA. However, at high operating frequencies

(12 MHz) the 80CL51 consumes far more energy (18 mA typ)

than the AD8802/AD8804 and TMP14 combined. Therefore,

to achieve a low power design the 80CL51 should operate at its

lowest possible frequency or be placed in its power-down mode

at the end of each instruction sequence.

To use the power-down mode of the 80CL51

µC set PCON.1

as the last instruction executed prior to going into the power-

down mode. If INT2 and INT9 are enabled, the 80CL51

µC

can be awakened from power-down mode with external inter-

rupts. As shown in Figure 28, the TLC555 outputs a pulse

every few seconds providing the interrupt to restart the 80CL51

µC which then samples the user input pins, the outputs of the