AD7856ARS datasheet(26/32 Pages) AD

26 / 32 page

AD7856

–26–

REV. A

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.

START

POWER-ON, APPLY CLKIN SIGNAL,

WAIT 150ms FOR AUTOMATIC CALIBRATION

APPLY

SYNC (IF REQUIRED), SCLK,

WRITE TO CONTROL REGISTER

SETTING CHANNEL AND TWO-WIRE MODE

PULSE

CONVST PIN

WAIT FOR BUSY SIGNAL TO GO LOW

WAIT FOR BUSY BIT = 0

SERIAL

INTERFACE

MODE

READ

DATA

DURING

CONVERSION

YES

APPLY

SYNC (IF REQUIRED), SCLK, READ

CURRENT CONVERSION RESULT ON DIN PIN

APPLY

SYNC (IF REQUIRED), SCLK, READ

PREVIOUS CONVERSION RESULT ON DIN PIN

WAIT APPROX. 200 ns AFTER

CONVST RISING EDGE OR AFTER END

OF CONTROL REGISTER WRITE

Figure 34. Flowchart for Setting Up, Reading and Writing in Interface Mode 1

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 DVDD. Where reference is made to the

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.

AD7856ARS Datasheet(PDF) 26 Page - Analog Devices

AD7856ARS Datasheet(HTML) 26 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Datasheet Download

Link URL