AD7699

Rev. 0 | Page 22 of 28

GENERAL TIMING WITHOUT A BUSY INDICATOR

Figure 35 details the timing for all three modes: reading/writing

during conversion, after conversion, and spanning conversion.

Note that the gating item for both CFG and data readback is at

the end of conversion (EOC). At the end of conversions (EOC),

if CNV is high, the busy indicator is disabled.

As detailed previously, the data access should occur up to safe

written to prior to EOC, it is discarded and the current

configuration remains. If the conversion result is not read out

fully prior to EOC, it is lost as the ADC updates SDO with the

MSB of the current conversion. For detailed timing, refer to

Figure 36 and Figure 37, which depict reading/writing spanning

conversion with all timing details, including setup, hold, and SCK.

When CNV is brought low after EOC, SDO is driven from high

impedance to the MSB. Falling SCK edges clock out bits starting

with MSB − 1.

The SCK can idle high or low depending on the clock polarity

(CPOL) and clock phase (CPHA) settings if SPI is used. A simple

solution is to use CPOL = CPHA = 0 as shown in Figure 35 with

SCK idling low.

PHASE

CNV

CNV

CNV

DIN

SDO

DIN

SDO

DIN

SDO

SCK

SCK

SCK

NOTES

1. CNV MUST BE HIGH PRIOR TO THE END OF CONVERSION (EOC) TO AVOID THE BUSY INDICATOR.

A TOTAL OF 16 SCK FALLING EDGES IS REQUIRED TO RETURN SDO TO HIGH-Z. IF CFG READBACK

IS ENABLED, A TOTAL OF 30 SCK FALLING EDGES IS REQUIRED TO RETURN SDO TO HIGH-Z.

1

ACQUISITION

(n – 1)

ACQUISITION

(n)

ACQUISITION

(n + 1)

ACQUISITION

(n + 2)

CONVERSION (n – 1)

CONVERSION (n)

CONVERSION (n + 1)

CONVERSION (n – 2)

DATA

(n – 2)

DATA

(n – 2)

DATA

(n – 1)

DATA

(n – 1)

DATA (n)

DATA (n)

DATA

(n + 1)

CFG (n)

CFG (n + 2)

CFG (n + 1)

CFG (n + 3)

1

16/30

1

16/30

1

16/30

1

16/30

1

16/30

1

16/30

1

16/30

1

1

16/30

1

16/30

1

16/30

DATA

(n – 2)

DATA

(n – 1)

DATA (n + 1)

DATA (n)

CFG (n)

CFG (n + 1)

CFG (n + 2)

CFG (n + 3)

XXX

DATA (n – 2)

DATA (n – 1)

DATA (n)

XXX

CFG (n)

CFG (n + 1)

CFG (n + 2)

MSB

(n – 1)

MSB

(n + 1)

MSB

(n)

MSB

(n – 2)

END OF CONVERSION (EOC)

START OF CONVERSION

EOC

EOC

POWER

UP

Figure 35. General Interface Timing for the AD7699 Without a Busy Indicator