Datasheet

AD7466/AD7467/AD7468
Rev. C | Page 22 of 28
SERIAL INTERFACE
Figure 29, Figure 30, and Figure 31 show the timing diagrams
for serial interfacing to the AD7466/AD7467/AD7468. The
serial clock provides the conversion clock and controls the
transfer of information from the ADC during a conversion.
The part begins to power up on the
CS
falling edge. The falling
edge of
CS
puts the track-and-hold into track mode and takes
the bus out of three-state. The conversion is also initiated at this
point. On the third SCLK falling edge after the
CS
falling edge,
the part should be powered up fully at Point B, as shown in
Figure 29, and the track-and-hold returns to hold.
For the AD7466, the SDATA line goes back into three-state and
the part enters power-down on the 16th SCLK falling edge. If
the rising edge of
CS
occurs before 16 SCLKs elapse, the
conversion terminates, the SDATA line goes back into three-
state, and the part enters power-down; otherwise SDATA
returns to three-state on the 16th SCLK falling edge, as shown
in
Figure 29. Sixteen serial clock cycles are required to perform
the conversion process and to access data from the AD7466.
For the AD7467, the 14th SCLK falling edge causes the SDATA
line to go back into three-state, and the part enters power-down.
If the rising edge of
CS
occurs before 14 SCLKs elapse, the con-
version terminates, the SDATA line goes back into three-state,
and the AD7467 enters power-down; otherwise SDATA returns
to three-state on the 14th SCLK falling edge, as shown in
Figure 30.
Fourteen serial clock cycles are required to perform the
conversion process and to access data from the AD7467.
For the AD7468, the 12th SCLK falling edge causes the SDATA
line to go back into three-state, and the part enters power-
down. If the rising edge of
CS
occurs before 12 SCLKs elapse,
the conversion terminates, the SDATA line goes back into three-
state, and the AD7468 enters power-down; otherwise SDATA
returns to three-state on the 12th SCLK falling edge, as shown
in
Figure 31. Twelve serial clock cycles are required to perform
the conversion process and to access data from the AD7468.
CS
going low provides the first leading zero to be read in by the
microcontroller or DSP. The remaining data is then clocked out
by subsequent SCLK falling edges, beginning with the second
leading zero; thus, the first clock falling edge on the serial clock
has the first leading zero provided and also clocks out the
second leading zero. For the AD7466, the final bit in the data
transfer is valid on the 16th SCLK falling edge, having been
clocked out on the previous (15th) SCLK falling edge.
In applications with a slow SCLK, it is possible to read in data
on each SCLK rising edge. In such a case, the first falling edge
of SCLK after the
CS
falling edge clocks out the second leading
zero and can be read in the following rising edge. If the first
SCLK edge after the
CS
falling edge is a falling edge, the first
leading zero that was clocked out when
CS
went low is missed,
unless it is not read on the first SCLK falling edge. The 15th
falling edge of SCLK clocks out the last bit, and it can be read in
the following rising SCLK edge.
If the first SCLK edge after the
CS
falling edge is a rising edge,
CS
clocks out the first leading zero, and it can be read on the SCLK
rising edge. The next SCLK falling edge clocks out the second
leading zero, and it can be read on the following rising edge.
SCLK
t
2
t
3
t
4
t
7
t
5
t
8
t
CONVERT
t
QUIET
DB11 DB10 DB2 DB1 DB0
B
4 LEADING ZEROS
13 14 15 16
t
1
THREE-STATE
THREE-STATE
S
DAT
A
CS
5
43
2
1
02643-030
t
6
12 BITS OF DATA
0
0
00
Figure 29. AD7466 Serial Interface Timing Diagram
t
QUIET
t
1
SCLK
S
DAT
A
4 LEADING ZEROS
THREE-STATE
THREE-STATE
10 BITS OF DATA
B
12345 1314
DB9 DB8 DB0
t
2
t
3
t
4
t
7
t
5
t
8
t
6
t
CONVERT
02643-031
CS
0
0
00
Figure 30. AD7467 Serial Interface Timing Diagram