REV. 0

AD7660

–16–

which results in a longer BUSY width. In read-during-conversion

mode, the serial clock and data toggle at appropriate instants,

which minimizes potential feedthrough between digital activity

and the critical conversion decisions.

SLAVE SERIAL INTERFACE

External Clock

The AD7660 is configured to accept an externally supplied

serial data clock on the SCLK pin when the EXT/

INT pin is

held high. In this mode, several methods can be used to read the

data. When

CS and RD are both low, the data can be read after

each conversion or during the following conversion. The exter-

nal clock can be either a continuous or discontinuous clock. A

discontinuous clock can be either normally high or normally low

when inactive. Figure 18 and Figure 20 show the detailed timing

diagrams of these methods. Usually, because the AD7660 has a

longer acquisition phase than the conversion phase, the data are

read immediately after conversion.

While the AD7660 is performing a bit decision, it is important

that voltage transients not occur on digital input/output pins or

degradation of the conversion result could occur. This is particu-

larly important during the second half of the conversion phase

because the AD7660 provides error correction circuitry that can

correct for an improper bit decision made during the first half of

the conversion phase. For this reason, it is recommended that when

an external clock is being provided, it is a discontinuous clock

that is toggling only when BUSY is low or, more importantly,

that it does not transition during the latter half of BUSY high.

BUSY

CS, RD

CNVST

SYNC

SCLK

SDOUT

12

3

14

15

16

D15

D14

D2

D1

D0

X

EXT/

INT = 0

RDC/SDIN = 0

INVSCLK = INVSYNC = 0

Figure 16. Master Serial Data Timing for Reading (Read after Convert)

EXT/

INT = 0

CS, RD

RDC/SDIN = 1

INVSCLK = INVSYNC = 0

CNVST

BUSY

SYNC

SCLK

SDOUT

D15

D14

D2

D1

D0

X

12

3

14

15

16

Figure 17. Master Serial Data Timing for Reading (Read Previous Conversion During Convert)