Preliminary Technical Data
SERIAL INTERFACE
AD7356
back into three-state on the 32nd SCLK falling edge or the rising
Figure 19 shows the detailed timing diagram for serial
interfacing to the AD7356. The serial clock provides the
conversion clock and controls the transfer of information from
the AD7356 during conversion.
CS
edge of , which ever occurs first.
A minimum of 14 serial clock cycles are required to perform
the conversion process and to access data from one conversion
CS
on either data line of the AD7356.
going low provides the
CS
The
signal initiates the data transfer and conversion process.
CS
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 a second leading zero. Thus, the first
falling clock edge on the serial clock has the leading zero
provided and also clocks out the second leading zero. The 12-bit
result then follows with the final bit in the data transfer valid on
the 14th falling edge, having being clocked out on the previous
(13th) falling edge. In applications with a slower SCLK, it may be
possible to read in data on each SCLK rising edge depending on
The falling edge of
puts the track and hold into hold mode at
which point the analog input is sampled and the bus is taken
out of three-state. The conversion is also initiated at this point
and requires a minimum of 14 SCL to complete. Once 13 SCLK
falling edges have elapsed, the track and hold will go back into
track on the next SCLK rising edge, as shown in Figure 19 at
point B. If a 16 bit data transfer is used on the AD7356, then
two trailing zeros will appear after the final LSB. On the rising
edge of , the conversion will be terminated and SDATAA and
SDATAB will go back into three-state. If
but is instead held low for a further 14 SCLK cycles on SDATAA,
the data from the conversion on ADCB will be output on
SDATAA.
CS
CS
the SCLK frequency. The first rising edge of SCLK after the
CS
is not brought high,
falling edge would have the second leading zero provided, and
the 13th rising SCLK edge would have DB0 provided.
CS
Likewise, is
is held low for a further 14 SCLK cycles on
SDATAA, the data from the conversion on ADCA will be output
on SDATAB. This is illustrated in Figure 20 where the case for
SDATAA is shown. In this case, the SDATA line in use will go
tACQUISITION
CS
t9
tCONVERT
t2
t6
B
SCLK
3
4
5
1
2
13
t5
tQUIET
t8
t7
t3
t4
D
D
A
B
OUT
OUT
0
DB11
DB10
DB2
0
DB9
DB8
DB1
DB0
THREE-STATE
THREE-
STATE
2 LEADING ZEROS
Figure 19. Serial Interface Timing Diagram
CS
t6
t2
SCLK
3
4
5
1
2
14
15
16
17
32
t5
t10
t3
t4
t7
DB11
DB10
DB9
DB11
B
0
ZERO
ZERO
ZERO
ZERO
ZERO
ZERO
ZERO
D
A
A
A
A
OUT
THREE-
STATE
THREE-
STATE
2 TRAILING ZEROS
2 LEADING ZEROS
2 LEADING
ZEROS
2 TRAILING ZEROS
Figure 20. Reading Data from Both ADCs on One SDATA Line with 32 SCLKs
Rev. PrC | Page 15 of 18