AD7856 Analog Devices, AD7856 Datasheet - Page 25

• Manufacturer Part Number: AD7856
• Description: 5 V Single-Supply, 8-Channel, 14-Bit, 285 kSPS, Serial Sampling ADC
• Manufacturer: Analog Devices

Specifications of AD7856

• Resolution (bits): 14bit
• # Chan: 8
• Sample Rate: 285kSPS
• Interface: Ser,SPI
• Analog Input Type: SE-Uni
• Ain Range: (Vref) p-p,Uni (Vref)
• Adc Architecture: SAR
• Pkg Type: DIP,SOIC,SOP

Mode 2 (3-Wire SPI/QSPI Interface Mode)
This is the DEFAULT INTERFACE MODE.
In Figure 33 below we have the timing diagram for interface
Mode 2, which is the SPI/QSPI interface mode. Here the SYNC
input is active low and may be pulsed or permanently tied low.
If SYNC is permanently low, 16 clock pulses must be applied to
the SCLK pin for the part to operate correctly otherwise, with a
pulsed SYNC input, a continuous SCLK may be applied pro-
vided SYNC is low for only 16 SCLK cycles. In Figure 33 the
REV. A
Figure 33. SPI/QSPI Mode 2 Timing Diagram for Read/Write Operation with DIN Input
DOUT Output and SYNC Input
DOUT (O/P)
DIN (I/P)
POLARITY PIN LOGIC HIGH
SYNC (I/P)
SCLK (I/P)
THREE-
STATE
t
5
t
3
DB15
t
1
7
t
t
t
3
6
11
= –0.4
= 45/75ns MAX (A/K),
= 30ns MIN (NONCONTINUOUS SCLK), 30/0.4
DB15
t
6
t
DB14
SCLK
t
2
8
DB14
MIN (NONCONTINUOUS SCLK) –/+0.4
t
9
DB13
t
3
10
t
DB13
7
= 30/40ns MIN (A/K),
–25–
DB12
4
t
DB12
6
SYNC going low disables the three-state on the DOUT pin. The
first falling edge of the SCLK after the SYNC going low clocks
out the first leading zero on the DOUT pin. The DOUT pin is
three-stated again a time, t
the DIN pin the data input has to be set up a time, t
SCLK rising edge as the part samples the input data on the
SCLK rising edge in this case. If resetting the interface is re-
quired, the SYNC must be taken high and then low.
DB11
5
DB11
t
8
t
SCLK
= 20ns MIN,
t
t
8
DB10
SCLK
ns MIN/MAX (CONTINUOUS SCLK)
6
ns MIN/MAX (CONTINUOUS SCLK),
DB10
12
DB0
, after the SYNC goes high. With
16
DB0
t
11
THREE-
STATE
t
12
AD7856
7
, before the