AD8802 Datasheet, PDF (13/16 Pages) Analog Devices – 12 Channel, 8-Bit TrimDACs with Power Shutdown

AD8802/AD8804
*
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
REV. 0
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