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AD7903

Data Sheet

Rev. A | Page 24 of 28

APPLICATIONS INFORMATION

SIMULTANEOUS SAMPLING

By having two unique user interfaces, the AD7903 provides

maximum flexibility with respect to how conversion results are

accessed from the device. The AD7903 provides an option for

the two user interfaces to share the convert start (CNVx) signal

from the digital host, creating a 2-channel, simultaneous sampling

device. In applications such as control applications, where latency

between the sampling instant and the availability of results in

the digital host is critical, it is recommended that the AD7903

be configured as shown in Figure 51. This configuration allows

simultaneous data reads, in addition to simultaneous sampling.

However, this configuration also requires an additional data

input pin on the digital host. This scenario allows the fastest

throughput because it requires only 15 or 16 SCKx falling edges

(depending on the status of the busy indicator) to acquire data

from the ADC.

Alternatively, for applications where simultaneous sampling is

required but pins on the digital host are limited, the two user

interfaces on the AD7903 can be connected in one of the daisy-

chain configurations shown in Figure 47 and Figure 49. This daisy

chaining allows the user to implement simultaneous sampling

functionality while requiring only one digital host input pin.

This scenario requires 31 or 32 SCKx falling edges (depending

on the status of the busy indicator) to acquire data from the ADC.

Figure 51 shows an example of a simultaneous sampling system

using two data inputs for the digital host. The corresponding

timing diagram in Figure 52 shows a CS mode, 3-wire simul-

taneous sampling serial interface without a busy indicator.

However, any of the 3-wire or 4-wire serial interface timing

options can be used.

Figure 51. Potential Simultaneous Sampling Connection Diagram

Figure 52. Potential Simultaneous Sampling Serial Interface Timing

VIO1

VIO2

CONVERT

DATA IN 2

CLK

DIGITAL HOST

DATA IN 1

AD7903

ADC2

SDI2

SDO2

CNV2

SCK2

AD7903

ADC1

SDI1

SDO1

CNV1

SCK1

SDIx = 1

tCNVH

tCONV

tCYC

CNVx

ACQUISITION

tACQ

tSCK

tSCKL

CONVERSION

SCKx

tEN

tHSDO

tDSDO

tDIS

tSCKH

SDO1

D15

D14

D13

SDO2

D15

D14

D13

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