EVAL-AD7791EBZ datasheet(18/21 Pages) AD

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Data Sheet

AD7791

Rev. A | Page 17 of 20

Continuous Read Mode

Rather than write to the communications register each time a

conversion is complete to access the data, the AD7791 can be

placed in continuous read mode. By writing 001111XX to the

communications register, the user needs only to apply the

appropriate number of SCLK cycles to the ADC and the 24-bit

word will automatically be placed on the DOUT/RDY line

when a conversion is complete.

When DOUT/RDY goes low to indicate the end of a conver-

sion, sufficient SCLK cycles must be applied to the ADC and

the data conversion will be placed on the DOUT/RDY line.

When the conversion is read, DOUT/RDY will return high

until the next conversion is available. In this mode, the data can

be read only once. Also, the user must ensure that the data-

word is read

before the next conversion is complete. If the user has not read

the conversion before the completion of the next conversion or

if insufficient serial clocks are applied to the AD7791 to read

the word, the serial output register is reset when the next con-

version is complete and the new conversion is placed in the

output serial register.

To exit the continuous read mode, the instruction 001110XX

must be written to the communications register while the RDY

pin is low. While in the continuous read mode, the ADC moni-

tors activity on the DIN line so that it can receive the

instruction to exit the continuous read mode. Additionally, a

reset will occur if 32 consecutive 1s are seen on DIN. Therefore,

DIN should be held low in continuous read mode until an in-

struction is to be written to the device.

04227-0-008

DIN

SCLK

DOUT/RDY

0x3C

DATA

Figure 15. Continuous Read

EVAL-AD7791EBZ Datasheet(PDF) 18 Page - Analog Devices