AD7904/AD7914/AD7924
Table II. Channel Selection
Analog Input Channel
IN0
SEQUENCER OPERATION
The configuration of the SEQ1 and SEQ0 bits in the control
register allows the user to select a particular mode of operation
of the sequencer function. Table IV outlines the three modes of
operation of the Sequencer.
ADD1
ADD0
0
0
1
1
0
1
0
1
V
VIN
IN2
VIN
1
V
Figure 2 reflects the traditional operation of a multichannel ADC,
where each serial transfer selects the next channel for conversion.
In this mode of operation the Sequencer function is not used.
3
Table III. Power Mode Selection
PM1 PM0 Mode
Figure 3 shows how to program the AD7904/AD7914/AD7924
to continuously convert on a sequence of consecutive channels
from Channel 0 to a selected final channel. To exit this mode of
operation and revert back to the traditional mode of operation of a
multichannel ADC (as outlined in Figure 2), ensure that the
WRITE bit = 1 and SEQ1 = SEQ0 = 0 on the next serial transfer.
1
1
1
Normal Operation. In this mode, the AD7904/
AD7914/AD7924 remain in full power mode
regardless of the status of any of the logicinputs.
This mode allows the fastest possible throughput
rate from the AD7904/AD7914/AD7924.
Table IV. Sequence Selection
SEQ1 SEQ0 Sequence Type
0
Full Shutdown. In this mode, the AD7904/
AD7914/AD7924 is in full shutdown mode with all
circuitry on the AD7904/AD7914/AD7924
powering down. The AD7904/AD7914/AD7924
retains the information in the Control Register
while in full shutdown. The part remains in full
shutdown until these bits are changed.
0
X
This configuration means that the sequence
function is not used. The analog input channel
selected for each individual conversion is
determined by the contents of the channel
address bits ADD1, ADD0 in each prior write
operation. This mode of operation reflects the
traditional operation of a multichannel ADC,
without the Sequencer function being used, where
each write to the AD7904/AD7914/AD7924
selects the next channel for conversion
(see Figure 2).
0
0
1
0
Auto Shutdown. In this mode, the AD7904/
AD7914/AD7924/ automatically enters full
shutdown mode at the end of each conversion
when the control register is updated. Wake-up
time from full shutdown is 1 µs and the user
should ensure that 1µs has elapsed before
attempting to perform a valid conversion on the
part in this mode.
1
1
0
1
If the SEQ1 and SEQ0 bits are set in this way
then the sequence function will not be interrupted
upon completion of the WRITE operation. This
allows other bits in the Control Register to be
altered between conversions while in a sequence
without terminating the cycle.
Invalid Selection. This configuration is not allowed.
This configuration is used in conjunction with
the channel address bits ADD1, ADD0 to
program continuous conversions on a consecutive
sequence of channels from Channel 0 to a selected
final channel as determined by the channel
address bits in the Control Register (see Figure 3).
–14–
REV. 0
ADI [ ADI ]
