AD7851 Analog Devices, AD7851 Datasheet - Page 25

• Manufacturer Part Number: AD7851
• Description: 14-Bit, 333 kSPS, Serial Sampling A/D Converter
• Manufacturer: Analog Devices

Specifications of AD7851

• Resolution (bits): 14bit
• # Chan: 1
• Sample Rate: 333kSPS
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: (Vref) p-p,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: DIP,SOIC,SOP

DETAILED TIMING SECTION
Mode 1 (2-Wire 8051 Interface)
The read and writing takes place on the DIN line and the conver-
sion is initiated by pulsing the CONVST pin (note that in every
write cycle the 2/3 MODE bit must be set to 1). The conversion
may be started by setting the CONVST bit in the control register
to 1 instead of using the CONVST line.
Below in Figure 33 and in Figure 34 are the timing diagrams for
Interface Mode 1 in the 2-wire interface mode. Here the DIN pin
is used for both input and output as shown. The SYNC input is
level-triggered active low and can be pulsed (Figure 33) or can be
constantly low (Figure 34).
In Figure 33, the part samples the input data on the rising edge
of SCLK. After the 16th rising edge of SCLK, the DIN is con-
figured as an output. When the SYNC is taken high, the DIN is
three-stated. Taking SYNC low disables the three-state on the
DIN pin and the first SCLK falling edge clocks out the first data
bit. Once the 16 clocks have been provided, the DIN pin will
automatically revert back to an input after a time t
REV. B
Figure 33. Timing Diagram for Read/Write Operation with DIN as an Input/Output (Interface Mode 1, SM1 = SM2 = 0)
Figure 34. Timing Diagram for Read/Write Operation with DIN as an Input/Output and SYNC Input Tied Low
(Interface Mode 1, SM1 = SM2 = 0)
SCLK (I/P)
SYNC (I/P)
SCLK (I/P)
DIN (I/O)
DIN (I/O)
POLARITY PIN
LOGIC HIGH
POLARITY PIN
LOGIC HIGH
t
3
DB15
DB15
t
t
7
7
1
1
t
t
3
6
= –0.4 t
= 45 MAX, t
DATA WRITE
DATA WRITE
t
t
6
13
= 45 MAX, t
= 90 MAX, t
t
t
8
8
SCLK
7
MIN (NONCONTINUOUS SCLK)
= 30ns MIN, t
14
7
. Note that a
DIN BECOMES AN OUTPUT
14
= 30ns MIN, t
DB0
DB0
= 50ns MAX
16
16
t
11
8
= 20 MIN
t
13
t
12
8
= 20 MIN,
–25–
THREE-STATE
continuous SCLK shown by the dotted waveform in Figure 33
can be used provided the SYNC is low for only 16 clock pulses
in each of the read and write cycles. The POLARITY pin may
be used to change the SCLK edge which the data is sampled on
and clocked out on.
In Figure 34, the SYNC line is tied low permanently, which
results in a different timing arrangement. With SYNC tied low
permanently, the DIN pin will never be three-stated. The 16th
rising edge of SCLK configures the DIN pin as an input or an
output as shown in the diagram. Here no more than 16 SCLK
pulses must occur for each of the read and write operations.
If reading from and writing to the calibration registers in this
interface mode, all the selected calibration registers must be
read from or written to. The read and write operations cannot
be aborted. When reading from the calibration registers, the
DIN pin will remain as an output for the full duration of all
the calibration register read operations. When writing to the
calibration registers, the DIN pin will remain as an input for
the full duration of all the calibration register write operations.
t
5A
t
3
0.4 t
1
SCLK
1
t
DB15
t
DB15
6
6
MIN/MAX (CONTINUOUS SCLK),
DATA READ
6
DATA READ
t
t
6
6
16
16
DIN BECOMES AN INPUT
DIN BECOMES AN INPUT
DB0
DB0
t
11
t
t
14
14
AD7851