AD7739 datasheet(24/32 Pages) AD

24 / 32 page

AD7739

Rev. 0 | Page 24 of 32

CONTINUOUS CONVERSION MODE

When the mode register is being written, the ADC status byte is

cleared and the RDY pin goes high, regardless of its previous

state. When the continuous conversion command is written to

the mode register, the ADC starts conversion on the channel

selected by the address of the mode register.

After the conversion is complete, the relevant channel data

RDY bit in the ADC status register is set, and the AD7739

continues converting on the next enabled channel. The part will

cycle through all enabled channels until put into another mode

or reset. The cycle period will be the sum of all enabled

channels’ conversion times, set by the corresponding channel

conversion time registers.

The RDY bit is reset when the relevant channel data register is

being read. The behavior of the RDY pin depends on the

RDYFN bit in the I/O port register. When the RDYFN bit is 0,

the RDY pin goes low when any channel has unread data. When

the RDYFN bit is set to 1, the RDY pin will go low only if all

enabled channels have unread data.

If an ADC conversion result has not been read before a new

ADC conversion is completed, the new result will overwrite the

previous one. The relevant RDY bit goes low and the RDY pin

goes high for at least 163 MCLK cycles (~26.5 µs), indicating

when the data register is updated, and the previous conversion

data is lost.

If the data register is being read as an ADC conversion

completes, the data register will not be updated with the new

result (to avoid data corruption) and the new conversion

data is lost.

Figure 19 shows the digital interface signal’s sequence for the

continuous conversion mode with Channels 0 and 1 enabled

and the RDYFN bit set to 0. The RDY pin goes low and the data

sequence but with the RDYFN bit set to 1. The RDY pin goes

low and all data registers are read after all conversions are

completed. Figure 21 shows the RDY pin when no data is read

from the AD7739.

SERIAL

INTERFACE

START

CONTINUOUS

CONVERSION

RDY

CH0 CONVERSION

READ

DATA

CH1

CH1 CONVERSION

CH0 CONVERSION

READ

DATA

CH0

CH1 CONVERSION

READ

DATA

CH0

CH0 CONVERSION

READ

DATA

CH1

03742-0-019

Figure 19. Continuous Conversion, CH0 and CH1, RDYFN = 0

SERIAL

INTERFACE

START

CONTINUOUS

CONVERSION

RDY

CH0 CONVERSION

READ

DATA

CH1

CH1 CONVERSION

CH0 CONVERSION

READ

DATA

CH0

CH1 CONVERSION

READ

DATA

CH0

CH0 CONVERSION

READ

DATA

CH1

03742-0-020

Figure 20. Continuous Conversion, CH0 and CH1, RDYFN = 1

SERIAL

INTERFACE

START

CONTINUOUS

CONVERSION

RDY

CH0 CONVERSION

CH1 CONVERSION

CH0 CONVERSION

CH1 CONVERSION

CH0 CONVERSION

03742-0-021

Figure 21. Continuous Conversion, CH0 and CH1, No Data Read

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