AD7851ARS datasheet(28/36 Pages) AD

28 / 36 page

AD7851

–28–

REV. B

If the user has control of the

CONVST pin but does not want to

exercise it for every conversion, the control register may be used

to start a conversion. Setting the

CONVST bit in the control

trol of the

CONVST pin, a conversion should not be initiated

by writing to the control register. The reason for this is that the

user may get locked out and not be able to perform any further

write/read operations. When a conversion is started by writing to

the control register, the

SYNC goes low and read/write opera-

tions take place while the conversion is in progress. However,

once the conversion is complete, there is no way of writing to

the part unless the

CONVST pin is exercised. The CONVST

signal triggers the

SYNC signal low which allows read/write

operations to take place.

SYNC must be low to perform read/

write operations. The

SYNC is triggered low by the CONVST

signal rising edge or by setting the

CONVST bit in the control

CONVST pin, the user may become locked out.

SERIAL

INTERFACE

MODE

POWER ON, APPLY CLKIN SIGNAL,

WAIT FOR AUTOMATIC CALIBRATION

DIN CONNECTED TO DGND

YES

START

WAIT FOR BUSY SIGNAL

TO GO LOW

PULSE

CONVST PIN

READ

DATA

DURING

CONVERSION

WAIT APPROXIMATELY 200ns

AFTER

CONVST RISING EDGE

APPLY

SYNC (IF REQUIRED), SCLK, AND READ

CONVERSION RESULT ON DOUT PIN

PULSE

CONVST PIN

SYNC AUTOMATICALLY GOES LOW

AFTER

CONVST RISING EDGE

SCLK AUTOMATICALLY ACTIVE, READ

CONVERSION RESULT ON DOUT PIN

4, 5

2, 3

Figure 40. Flowchart for Setting Up and Reading from the AD7851

CONFIGURING THE AD7851

AD7851 as a Read-Only ADC

The AD7851 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. Figure 40 outlines the

sequence used to configure the AD7851 as a read-only ADC. In

this case, there is no writing to the on-chip registers and only the

conversion result data is read from the part. Interface Mode 1

cannot be used in this case as it is necessary to write to the con-

trol register to set Interface Mode 1. 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 automatic

calibration will be completed approximately 42 ms after the

AD7851 has powered up (6 MHz CLK).

AD7851ARS Datasheet(PDF) 28 Page - Analog Devices

AD7851ARS Datasheet(HTML) 28 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 33 34 35 36

Datasheet Download

Link URL