Datasheet

Data Sheet AD7607
Rev. B | Page 25 of 32
Figure 42 shows a read of eight simultaneous conversion results
using two D
OUT
lines on the AD7607. In this case, a 56 SCLK
transfer is used to access data from the AD7607, and
CS
is held
low to frame the entire 56 SCLK cycles. Data can also be clocked
out using just one D
OUT
line; in which case, it is recommended
that D
OUT
A be used to access all conversion data because the
channel data is output in ascending order. For the AD7607 to
access all eight conversion results on one D
OUT
line, a total of
112 SCLK cycles are required. These 112 SCLK cycles can be
framed by one
CS
signal, or each group of 14 SCLK cycles can be
individually framed by the
CS
signal. The disadvantage of using
just one D
OUT
line is that the throughput rate is reduced
if reading occurs after conversion. The unused D
OUT
line should
be left unconnected in serial mode. If D
OUT
B is to be used as a
single D
OUT
line, the channel results are output in the following
order: V5, V6, V7, V8, V1, V2, V3, and V4; however, the
FRSTDATA indicator returns low after V5 is read on D
OUT
B.
Figure 6 shows the timing diagram for reading one channel of
data, framed by the
CS
signal, from the AD7607 in serial mode.
The SCLK input signal provides the clock source for the serial
read operation. The
CS
goes low to access the data from the
AD7607. The falling edge of
CS
takes the bus out of three-state
and clocks out the MSB of the 14-bit conversion result. This
MSB is valid on the first falling edge of the SCLK after the
CS
falling edge.
The subsequent 13 data bits are clocked out of the AD7607 on the
SCLK rising edge. Data is valid on the SCLK falling edge. To access
each conversion result, 14 clock cycles must be provided.
The FRSTDATA output signal indicates when the first channel,
V1, is being read back. When the
CS
input is high, the FRSTDATA
output pin is in three-state. In serial mode, the falling edge of
CS
takes FRSTDATA out of three-state and sets the FRSTDATA pin
high, indicating that the result from V1 is available on the D
OUT
A
output data line. The FRSTDATA output returns to a logic low
following the 14
th
SCLK falling edge. If all channels are read on
D
OUT
B, the FRSTDATA output does not go high when V1 is output
on this serial data output pin. It goes high only when V1 is available
on D
OUT
A (and this is when V5 is available on D
OUT
B).
READING DURING CONVERSION
Data can be read from the AD7607 while BUSY is high and the
conversions are in progress. This has little effect the performance
of the converter, and it allows a faster throughput rate to be
achieved. A parallel, parallel byte, or serial read can be performed
during conversions and when oversampling is or is not enabled.
Figure 3 shows the timing diagram for reading while BUSY is
high in parallel or serial mode. Reading during conversions
allows the full throughput rate to be achieved when using the
serial interface with V
DRIVE
above 3.3 V.
Data can be read from the AD7607 at any time other than on
the falling edge of BUSY because this is when the output data
registers get updated with the new conversion data. Time t
6
, as
outlined in Table 3, should be observed in this condition.
V1 V4V2 V3
V5
V8V6 V7
SCLK
D
OUT
A
D
OUT
B
CS
56
08096-042
Figure 42. Serial Interface with Two D
OUT
Lines