AD7856 Analog Devices, AD7856 Datasheet - Page 26

• 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

AD7856
CONFIGURING THE AD7856
The AD7856 contains 14 on-chip registers that can be accessed
via the serial interface. In the majority of applications it will not
be necessary to access all of these registers. Here the CLKIN
signal is applied directly after power-on, the CLKIN signal must
be present to allow the part to perform a calibration. This auto-
matic calibration will be completed approximately 150 ms
after power-on.
Writing to the AD7856
For accessing the on-chip registers it is necessary to write to the
part. To change the channel from the default channel setting the
user will be required to write to the part. To enable Serial Inter-
face Mode 1 the user must also write to the part. Figures 34 and
35 outline flowcharts of how to configure the AD7856 Serial
Interface Modes 1 and 2 respectively. The continuous loops on
all diagrams indicate the sequence for more than one conversion.
Figure 34. Flowchart for Setting Up, Reading and Writing in Interface Mode 1
PREVIOUS CONVERSION RESULT ON DIN PIN
APPLY SYNC (IF REQUIRED), SCLK, READ
CONVST RISING EDGE OR AFTER END
OF CONTROL REGISTER WRITE
WAIT APPROX. 200 ns AFTER
–26–
WAIT 150ms FOR AUTOMATIC CALIBRATION
CURRENT CONVERSION RESULT ON DIN PIN
The options of using a hardware (pulsing the CONVST pin) or
software (setting the CONVST bit to 1) conversion start, and
reading/writing during or after conversion are shown in Figures
34 and 35. If the CONVST pin is never used, it should be
permanently tied to DV
BUSY bit equal to a Logic 0, to indicate the end of conversion,
the user in this case would poll the BUSY bit in the status register.
Interface Mode 1 Configuration
Figure 34 shows the flowchart for configuring the part in Inter-
face Mode 1. This mode of operation can only be enabled by
writing to the control register and setting the 2/3 MODE bit.
Reading and writing cannot take place simultaneously in this
mode as the DIN pin is used for both reading and writing.
Initiating conversions in software is not recommended in this
mode, see Detailed Timing section.
SETTING CHANNEL AND TWO-WIRE MODE
APPLY SYNC (IF REQUIRED), SCLK, READ
WAIT FOR BUSY SIGNAL TO GO LOW
POWER-ON, APPLY CLKIN SIGNAL,
APPLY SYNC (IF REQUIRED), SCLK,
WRITE TO CONTROL REGISTER
YES
WAIT FOR BUSY BIT = 0
PULSE CONVST PIN
CONVERSION
INTERFACE
DURING
START
SERIAL
READ
DATA
MODE
OR
?
?
1
NO
DD
. Where reference is made to the
REV. A