AD7656 datasheet(20/25 Pages) AD

20 / 25 page

AD7658/AD7657/AD7656

Preliminary Technical Data

Rev. PrI | Page 20 of 25

DOUTA

DOUTB

SCLK

Figure 10. Serial Interface with two DOUT lines.

Serial Read Operation

Figure 11 shows the timing diagram for reading data from the

AD7658/AD7657/AD7656 in serial mode. The SCLK input

signal provides the clock source for the serial interface. The CS

signal goes low to access data from the

AD7658/AD7657/AD7656. The falling edge of CS takes the bus

out of three-state and clocks out the MSB of the 12/14/16-bit

conversion result. The ADCs output 16- bits for each conversion

result. The data stream of the AD7658 consists of four leading

zeros followed by 12 bits of conversion data provided MSB first;

the data stream of the AD7657 consists of two leading zeros,

followed by the 14-bits of conversion data provided MSB first;

the data stream of the AD7656 consists of sixteen bits of

conversion data provided MSB first. The first bit of the

conversion result is valid on the first SCLK falling edge after the

CS falling edge. The subsequent 15 data bits of the data are

clocked out on rising edge of the SCLK signal. Data is valid on

the SCLK falling edge. Sixteen clock pulses must be provided to

the AD7658/AD7657/AD7656 to access each conversion result.

Figure 11 shows how a 16 SCLK read is used to access the

conversion results.

tCONV

tACQ

tQUIET

t17

t18

t19

t20

t21

t23

CONVST A/B/C

BUSY

ACQUISITION

CONVERSION

ACQUISITION

SCLK

DOUT A/B/C

DB15

DB14

DB13

DB1

DB0

Figure 11. Serial Read Operation

Daisy-Chain Mode(DCEN =1, SER/PAR = 1)

When reading conversion data back from the

AD7658/AD7657/AD7656 using the three/two DOUT pins it is

possible to Configure the AD7658/AD7657/AD7656 to operate

in Daisy-Chain Mode, using the DCEN pin. This Daisy-Chain

feature allows multiple AD7658/AD7657/AD7656 devices to be

cascaded together. This feature is useful for reducing

component count and wiring connections. An example

connection of two devices is shown in Figure 12, this

configuration shows two DOUT lines being used. Simultaneous

sampling of the 12 Analog Inputs is possible by using a

common CONVST signal. The DB5, DB4 and DB3 data pins are

used as Data input pins, DCIN[A:C], for the Daisy-Chain Mode.

The rising edge of CONVST is used to initiate a conversion on

the AD7658/AD7657/AD7656. After the BUSY signal has gone

low to indicate the conversion is complete the user can begin to

read the data from the two devices. Figure 13 shows the serial

timing diagram when operating two AD7658/AD7657/AD7656

AD7656 数据表(PDF) 20 Page - Analog Devices

AD7656 数据表(HTML) 20 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

数据表下载