AD7858/AD7858L

REV. B

–27–

Interface Mode 2 Configuration

Figure 35 shows the flowchart for configuring the part in Inter-

face Mode 2. In this case 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 transferring data during con-

version Note 1 must be obeyed.

APPLY

SYNC (IF REQUIRED), SCLK, WRITE

TO CONTROL REGISTER SETTING CHANNEL,

(SEE NOTE 1)

INITIATE

CONVERSION

IN

SOFTWARE

?

START

POWER-ON, APPLY CLKIN SIGNAL,

WAIT FOR AUTOMATIC CALIBRATION

PULSE

CONVST PIN

WAIT FOR BUSY SIGNAL TO GO LOW

OR

WAIT FOR BUSY BIT = 0

NO

SERIAL

INTERFACE

MODE

?

TRANSFER

DATA DURING

CONVERSION

?

NO

YES

YES

APPLY

SYNC (IF REQUIRED), SCLK,

READ CURRENT CONVERSION RESULT

ON DOUT PIN, AND WRITE CHANNEL

SELECTION

NOTES

WRITE OPERATION EXTENDS BEYOND THE FALLING EDGE OF 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.

THE ACQUISITION TIME (2

RESULT OF THIS CONVERSION SHOULD BE DISCARDED AND THE NEXT CONVERSION ON THAT SAME CHANNEL WILL PROVIDE CORRECT RESULTS.

WAIT APPROX 200ns AFTER

CONVST RISING EDGE

APPLY

SYNC (IF REQUIRED), SCLK, READ

PREVIOUS CONVERSION RESULT ON DOUT

PIN, AND WRITE CHANNEL SELECTION

NO

APPLY

SYNC (IF REQUIRED), SCLK, WRITE

TO CONTROL REGISTER SETTING CHANNEL

WAIT FOR BUSY SIGNAL TO GO LOW

OR

WAIT FOR BUSY BIT = 0

YES

2

WRITE TO CONTROL REGISTER SETTING

CONVST BIT TO 1, READ

CURRENT CONVERSION RESULT

ON DOUT PIN (SEE NOTE 2)

WRITE TO CONTROL REGISTER

SETTING CONVST BIT TO 1,

READ PREVIOUS RESULT ON

DOUT PIN (SEE NOTES 1&2)

TRANSFER

DATA DURING

CONVERSION

?

Figure 35. Flowchart for Setting Up, Reading, and Writing in Interface Mode 2