AD7983

Data Sheet

Rev. B | Page 18 of 24

CS MODE, 3-WIRE WITH BUSY INDICATOR

This mode is usually used when a single AD7983 is connected

to an SPI-compatible digital host that has an interrupt input.

The connection diagram is shown in Figure 28, and the

corresponding timing is given in Figure 29.

With SDI tied to VIO, a rising edge on CNV initiates a

conversion, selects the CS mode, and forces SDO to high

impedance. SDO is maintained in high impedance until the

completion of the conversion irrespective of the state of CNV.

Prior to the minimum conversion time, CNV can be used to

select other SPI devices, such as analog multiplexers, but CNV

must be returned low before the minimum conversion time

elapses and then held low for the maximum conversion time to

guarantee the generation of the busy signal indicator. When the

conversion is complete, SDO goes from high impedance to low.

With a pull-up on the SDO line, this transition can be used as an

interrupt signal to initiate the data read back controlled by the

digital host. The AD7983 then enters the acquisition phase and

goes into standby mode. The data bits are then clocked out,

MSB first, by subsequent SCK falling edges. The data is valid on

both SCK edges. Although the rising edge can be used to capture

the data, a digital host using the SCK falling edge allows a faster

reading rate provided it has an acceptable hold time. After the

optional 17th SCK falling edge or when CNV goes high,

whichever is earlier, SDO returns to high impedance.

If multiple AD7983s are selected at the same time, the SDO

output pin handles this contention without damage or induced

latch-up. Meanwhile, it is recommended that this contention be

kept as short as possible to limit extra power dissipation.

SDI

DATA IN

IRQ

DIGITAL HOST

CONVERT

CLK

VIO

VIO

47kΩ

CNV

SCK

Figure 28. CS Mode, 3-Wire with Busy Indicator

Connection Diagram (SDI High)

ACQUISITION

ACQUISITION

CONVERSION

SCK

CNV

SDI = 1

SDO

D15

D14

D1

D0

12

3

15

16

17

Figure 29. CS Mode, 3-Wire with Busy Indicator Serial Interface Timing (SDI High)