AD7634
Data Sheet
Rev. B | Page 24 of 32
INTERFACES
DIGITAL INTERFACE
The AD7634 has a versatile digital interface that can be set up as
either a serial or a parallel interface with the host system. The
serial interface is multiplexed on the parallel data bus. The AD7634
digital interface also accommodates 2.5 V, 3.3 V, or 5 V logic. In
most applications, the OVDD supply pin is connected to the host
system interface 2.5 V to 5.25 V digital supply. Finally, by using the
D0/OB/2C input pin, both twos complement or straight binary
coding can be used, except for in a 18-bit parallel interface.
Two signals, CS and RD, control the interface. When at least
one of these signals is high, the interface outputs are in high
impedance. Usually, CS allows the selection of each AD7634
in multicircuit applications and is held low in a single AD7634
design. RD is generally used to enable the conversion result on
the data bus.
RESET
The RESET input is used to reset the AD7634. A rising edge on
RESET aborts the current conversion (if any) and tristates the
data bus. The falling edge of RESET resets the AD7634 and clears
the data bus and configuration register. See
Figure 36 for the
RESET timing details.
t9
t8
RESET
DATA
BUS
BUSY
CNVST
0
6
406
-03
4
Figure 36. RESET Timing
PARALLEL INTERFACE
The AD7634 is configured to use the parallel interface when
the MODE[1:0] pins = 0, 1 or 2 for 18-/16-/8-bit interfaces,
respectively, as detailed in
Table 7.
Master Parallel Interface
Data can be continuously read by tying CS and RD low, thus
requiring minimal microprocessor connections. However, in
this mode, the data bus is always driven and cannot be used in
shared bus applications (unless the device is held in RESET).
t1
BUSY
DATA
BUS
PREVIOUS CONVERSION DATA
NEW DATA
CNVST
CS = RD = 0
t10
t4
t11
t3
0
6406
-035
Figure 37. Master Parallel Data Timing for Reading (Continuous Read)
Slave Parallel Interface
In slave parallel reading mode, the data can be read either after
each conversion, which is during the next acquisition phase, or
during the following conversion, as shown in
Figure 38 and
Figure 39, respectively. When the data is read during the conver-
sion, it is recommended that it is read-only during the first half
of the conversion phase. This avoids any potential feedthrough
between voltage transients on the digital interface and the most
critical analog conversion circuitry.
CURRENT
CONVERSION
t13
t12
BUSY
DATA
BUS
RD
CS
06
40
6-
03
6
Figure 38. Slave Parallel Data Timing for Reading (Read After Convert)
PREVIOUS
CONVERSION
t13
t12
t3
BUSY
DATA
BUS
CNVST,
RD
CS = 0
t4
t1
06
40
6-
0
37
Figure 39. Slave Parallel Data Timing for Reading (Read During Convert)