AD7280ABSTZ datasheet(45/48 Pages) AD

45 / 48 page

AD7280A

Rev. 0 | Page 45 of 48

If a second convert start signal is received by the AD7280A while

the conversion results are being read back, the data being read

back from the device, or chain of devices, can be corrupted. The

corruption of data occurs at the point in which the second con-

vert start signal is introduced. Any data read back prior to the

second convert start signal is correct, but data read back after

the second convert start signal may be corrupted.

Note that the corruption of data is not limited to the conversion

result. The device address, channel address, and CRC data can

also be corrupted. The CNVST control register should be used

to gate the convert start signal. This prevents any glitches that

occur on the CNVST pin from being applied directly to the

internal circuitry of the AD7280A.

SOFTWARE FLOWCHART

See Figure 41 for a software flowchart of a suggested sequence

of steps that should be considered when operating the

AD7280A in a noisy environment.

HAS THE

REQUIRED NUMBER

OF CONVERSIONS BEEN

COMPLETED?

YES

WAIT AT LEAST 5.5ms FOR ALL DEVICES

TO BE FULLY POWERED UP

POWER UP AD7280A

CHAIN OF DEVICES

INITIALIZE DEVICE IDs ON ALL

PARTS IN THE CHAIN

WRITE TO CONTROL REGISTER

TO RETURN DB1/DB2 TO

DEFAULT VALUES

PROGRAM CONFIGURATION

REGISTERS AS REQUIRED

INITIATE A

CONVERSION

WRITE TO CNVST CONTROL

CNVST PULSE THROUGH

READ BACK THE CONVERSION RESULTS FROM ALL DEVICES IN

THE DAISY-CHAIN READBACK MODE

CHECK

INTEGRITY OF

CHAIN INITIALIZATION

BY READING BACK THE LOW

BYTE OF THE CONTROL

ALL DEVICES

IS THE

CRC CORRECT

FOR ALL DATA FRAMES

READ BACK?

HAVE ANY

PARTS IN THE

CHAIN RETURNED A

RESULT OF ALL 0s FROM

THE CONTROL

NOT

YES

IGNORE RESPECTIVE

32-BIT FRAME

DATA VALIDATION

COMPLETE

YES

POWER DOWN AD7280A

CHAIN OF DEVICES

PLACE CHAIN IN POWER-DOWN MODE AND

WAIT AT LEAST 2ms FOR CAPACITORS ON

VREG AND VREF TO DISSIPATE CHARGE

Figure 41. Suggested Software Flowchart When Operating in a Noisy Environment

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