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AD7329 Datasheet(PDF) 35 Page - Analog Devices

Part No. AD7329
Description  1 MSPS, 8-Channel, Software-Selectable, True Bipolar Input, 12-Bit Plus Sign ADC
Download  40 Pages
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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AD7329 Datasheet(HTML) 35 Page - Analog Devices

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AD7329
Rev. 0 | Page 35 of 40
SERIAL INTERFACE
Figure 57 shows the timing diagram for the serial interface of
the AD7329. The serial clock applied to the SCLK pin provides
the conversion clock and controls the transfer of information to
and from the AD7329 during a conversion.
The CS signal initiates the data transfer and the conversion
process. The falling edge of CS puts the track-and-hold section
into hold mode and takes the bus out of three-state. The analog
input signal is then sampled. Once the conversion is initiated,
it requires 16 SCLK cycles to complete.
The track-and-hold section goes back into track mode on the
14th SCLK rising edge. On the 16th SCLK falling edge, the
DOUT line returns to three-state. If the rising edge of CS occurs
before 16 SCLK cycles have elapsed, the conversion is
terminated and the DOUT line returns to three-state. Depending
on where the CS signal is brought high, the addressed register
may be updated.
Data is clocked into the AD7329 on the SCLK falling edge. The
three MSBs on the DIN line are decoded to select which register
is addressed. The control register is a 12-bit register. If the
control register is addressed by the three MSBs, the data on the
DIN line is loaded into the control on the 15th SCLK rising edge.
If the sequence register or either of the range registers is
addressed, the data on the DIN line is loaded into the addressed
register on the 11th SCLK falling edge.
Conversion data is clocked out of the AD7329 on each SCLK
falling edge. Data on the DOUT line consists of three channel
identifier bits, a sign bit, and a 12-bit conversion result. The
channel identifier bits are used to indicate which channel
corresponds to the conversion result.
If the Weak/Three-State bit is set in the control register, rather
than returning to true three-state upon the 16th SCLK falling
edge, the DOUT line is pulled weakly to the logic level
corresponding to ADD3 of the next serial transfer. This is done
to ensure that the MSB of the next serial transfer is set up in
time for the first SCLK falling edge after the CS falling edge. If
the Weak/Three-State bit is set to 0 and the DOUT line returns
to true three-state between conversions, then depending on the
particular processor interfacing to the AD7329, the ADD3 bit
may be valid in time for the processor to clock it in successfully.
If the Weak/Three-State bit is set to 1, then although the DOUT
line has been driven to ADD3 since the previous conversion, it
is nevertheless so weakly driven that another device could take
control of the bus. This will not lead to a bus contention issue
because, for example, a 10 kΩ pull-up or pull-down resister is
sufficient to overdrive the logic level of ADD3. When the
Weak/Three-State bit is set to 1, the ADD3 is typically valid 9 ns
after the CS falling edge, compared with 14 ns when the DOUT
line returns to three-state at the end of the conversion.
ADD1
12
34
5
13
14
15
16
WRITE
REG
SEL1
REG
SEL2
LSB
0
MSB
ADD0
SIGN
DB11
DB10
DB2
DB1
DB0
t2
t6
t4
t9
t10
t3
t7
t5
t8
t1
tQUIET
tCONVERT
SCLK
CS
DOUT
THREE-
STATE
THREE-STATE
DIN
ADD2
3 IDENTIFICATION BITS
Figure 57. Serial Interface Timing Diagram (Control Register Write)


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