EVAL-AD7490SDZ データシートの表示（PDF） - Analog Devices

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EVAL-AD7490SDZ

16-Channel, 1 MSPS, 12-Bit ADC with Sequencer in 28-Lead TSSOP

Analog Devices 

AD7490

SHADOW REGISTER

The Shadow register on the AD7490 is a 16-bit, write-only

register. Data is loaded from the DIN pin of the AD7490 on the

falling edge of SCLK. The data is transferred on the DIN line at

the same time that a conversion result is read from the part.

This requires 16 serial falling edges for the data transfer. The

information is clocked into the Shadow register, provided the

SEQ and SHADOW bits are set to 0, 1, respectively, in the

previous write to the control register. MSB denotes the first bit

in the data stream. Each bit represents an analog input from

Channel 0 through Channel 15. A sequence of channels can be

selected through which the AD7490 cycles with each consecutive

CS falling edge after the write to the Shadow register. To select a

sequence of channels, the associated channel bit must be set for

each analog input. The AD7490 continuously cycles through

the selected channels in ascending order, beginning with the

lowest channel, until a write operation occurs (that is, the WRITE

bit is set to 1), with the SEQ and SHADOW bits configured in

any way except 1, 0 (see Table 9). The bit functions are outlined

in Table 10.

Figure 12 reflects the normal operation of a multichannel ADC,

where each serial transfer selects the next channel for conversion.

In this mode of operation, the sequencer function is not used.

POWER ON

DUMMY CONVERSIONS

DIN = ALL 1s

DIN: WRITE TO CONTROL REGISTER,

WRITE BIT = 1,

CS

SELECT CODING, RANGE, AND POWER MODE

SELECT CHANNEL ADD3 TO ADD0 FOR

CONVERSION,

SEQ = SHADOW = 0

DOUT: CONVERSION RESULT FROM

PREVIOUSLY SELECTED CHANNEL ADD3 TO

ADD0

CS

DIN: WRITE TO CONTROL REGISTER,

WRITE BIT = 1,

SEQ = SHADOW = 0

WRITE BIT = 1,

SELECT CODING, RANGE,AND POWER MODE

SELECT ADD3 TO ADD0 FOR CONVERSION,

SEQ = SHADOW = 0

Figure 12. SEQ Bit = 0, SHADOW Bit = 0 Flowchart

Data Sheet

Figure 13 shows how to program the AD7490 to continuously

convert on a particular sequence of channels using the Shadow

register. To exit this mode of operation and revert back to the

normal mode of operation of a multichannel ADC (as outlined

in Figure 12), ensure that WRITE = 1 and SEQ = SHADOW = 0

on the next serial transfer.

POWER ON

DUMMY CONVERSIONS

DIN = ALL 1s

DIN: WRITE TO CONTROL REGISTER,

WRITE BIT = 1,

CS

SELECT CODING, RANGE, AND POWER MODE

SELECT CHANNEL ADD3 TO ADD0 FOR

CONVERSION,

SEQ = 0 SHADOW = 1

CS

CS

WRITE

BIT = 0

DOUT: CONVERSION RESULT FROM

PREVIOUSLY SELECTED CHANNEL ADD3 TO

ADD0

DIN: WRITE TO SHADOW REGISTER,

SELECTING WHICH CHANNELS TO CONVERT

ON; CHANNELS SELECTED NEED NOT BE

CONSECUTIVE

WRITE BIT = 0

WRITE BIT = 1,

SEQ = 1, SHADOW = 0

CONTINUOUSLY

CONVERTS ON THE

SELECTED SEQUENCE

OF CHANNELS

WRITE BIT = 0

CONTINUOUSLY

CONVERTS ON THE

SELECTED SEQUENCE

OF CHANNELS BUT

ALLOWS RANGE,

CODING, AND SO ON,

TO CHANGE IN THE

CONTROL REGISTER

WITHOUT

INTERRUPTING THE

SEQUENCE PROVIDED,

SEQ = 1 SHADOW = 0

WRITE BIT = 1,

SEQ = 1,

SHADOW = 0

Figure 13. SEQ Bit = 0, SHADOW Bit = 1 Flowchart

Table 10. Shadow Register

MSB

LSB

15 14 13 12 11 10 9

8

7

6

5

4

3

2

1

0

VIN0 VIN1 VIN2 VIN3 VIN4 VIN5 VIN6 VIN7 VIN8 VIN9 VIN10 VIN11 VIN12 VIN13 VIN14 VIN15

Rev. D | Page 14 of 28

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