AD7983

Data Sheet

Rev. B | Page 16 of 24

DIGITAL INTERFACE

Though the AD7983 has a reduced number of pins, it offers

flexibility in its serial interface modes.

When in CS mode, the AD7983 is compatible with SPI, QSPI,

and digital hosts. This interface can use either a 3-wire or a 4-wire

interface. A 3-wire interface using the CNV, SCK, and SDO

signals minimizes wiring connections useful, for instance, in

isolated applications. A 4-wire interface using the SDI, CNV,

SCK, and SDO signals allows CNV, which initiates the conversions,

to be independent of the readback timing (SDI). This is useful

in low jitter sampling or simultaneous sampling applications.

The AD7983, when in chain mode, provides a daisy-chain

feature using the SDI input for cascading multiple ADCs on a

single data line similar to a shift register.

The mode in which the part operates depends on the SDI level

when the CNV rising edge occurs. The CS mode is selected if

SDI is high, and the chain mode is selected if SDI is low. The

SDI hold time is such that when SDI and CNV are connected,

the chain mode is always selected.

In either mode, the AD7983 offers the flexibility to optionally

force a start bit in front of the data bits. This start bit can be

used as a busy signal indicator to interrupt the digital host and

trigger the data reading. Otherwise, without a busy indicator,

the user must time out the maximum conversion time prior to

readback.

The busy indicator feature is enabled

• In CS mode if CNV or SDI is low when the ADC conversion

ends (see Figure 29 and Figure 33).

• In chain mode if SCK is high during the CNV rising edge

(see Figure 37).