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AD7851

–28–

REV. A

SERIAL

INTERFACE

MODE

YES

TRANSFER

DATA

DURING

CONVERSION

APPLY

SYNC (IF REQUIRED), SCLK, READ

CURRENT CONVERSION RESULT ON DOUT PIN,

AND WRITE ALL 0s ON DIN PIN

WAIT FOR BUSY SIGNAL TO GO LOW

OR WAIT FOR BUSY BIT = 0

APPLY

SYNC (IF REQUIRED), SCLK, WRITE TO CONTROL

CONVERSION RESULT ON DOUT PIN

2, 3

INITIATE

CONVERSION

SOFTWARE

WAIT APPROXIMATELY 200ns

AFTER

CONVST RISING EDGE

APPLY

SYNC (IF REQUIRED),

SCLK, READ PREVIOUS CONVERSION

RESULT ON DOUT PIN,

AND WRITE ALL 0s ON DIN PIN

YES

TRANSFER

DATA DURING

CONVERSION

APPLY

SYNC (IF REQUIRED), SCLK, WRITE TO CONTROL

CONVERSION RESULT ON DOUT PIN (SEE NOTE)

YES

NOTE:

WHEN USING THE SOFTWARE CONVERSION START AND TRANSFERRING

DATA DURING CONVERSION THE USER MUST ENSURE THE CONTROL

BUSY. THE FALLING EDGE OF BUSY RESETS THE CONVST BIT TO 0 AND

ONLY AFTER THIS TIME CAN IT BE REPROGRAMMED TO 1 TO START THE

NEXT CONVERSION.

START

POWER-ON, APPLY CLKIN SIGNAL,

WAIT 150ms FOR AUTOMATIC CALIBRATION

PULSE

CONVST PIN

WAIT FOR BUSY SIGNAL TO GO

LOW OR WAIT FOR BUSY BIT = 0

Figure 41. Flowchart for Setting Up, Reading, and Writing in Interface Modes 2 and 3

Writing to the AD7851

For accessing the on-chip registers it is necessary to write to the

part. To enable Serial Interface Mode 1, the user must also write

to the part. Figure 41 through 43 outline flowcharts of how to

configure the AD7851 for each of the different serial interface

modes. The continuous loops on all diagrams indicate the se-

quence for more than one conversion. 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 41 and 42. If the

CONVST

pin is never used then it should be tied to DVDD per-

manently. 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 Modes 2 and 3 Configuration

Figure 41 shows the flowchart for configuring the part in Inter-

face Modes 2 and 3. For these interface modes, the read and

write operations take place simultaneously via the serial port.

Writing all 0s ensures that no valid data is written to any of the

registers. When using the software conversion start and transfer-

ring data during conversion, Note must be obeyed.

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