AD5590BBC datasheet(39/44 Pages) AD

39 / 44 page

AD5590

Rev. 0 | Page 39 of 44

ADC Shadow Register

The shadow register on the ADC is a 16-bit, write-only register.

Data is loaded from the ADIN pin of the ADC on the falling

edge of ASCLK. The data is transferred on the ADIN line at the

same time as a conversion result is read from the ADC. This

requires 16 serial falling edges for the data transfer. The infor-

mation is clocked into the shadow register, provided that the

SEQ and shadow bits were set to 0 and 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 to Channel 15. A sequence of channels can

be selected through which the ADC cycles with each consecutive

ASYNC 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 ADC 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

). The bit

functions are outlined in

Table 25

Table 26

Figure 69 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.

Figure 70 shows how to program the ADC to continuously

convert on a particular sequence of channels. To exit this mode

of operation and revert back to the normal mode of operation

of a multichannel ADC (as outlined in Figure 69), ensure the

write bit = 1 and the SEQ = shadow = 0 on the next serial

transfer.

Figure 71 shows how a sequence of consecutive channels can

be converted without having to program the shadow register

or write to the ADC on each serial transfer. Again, to exit this

mode of operation and revert back to the normal mode of

operation of a multichannel ADC (as outlined in Figure 69),

ensure the write bit = 1 and the SEQ = shadow = 0 on

the next serial transfer.

ADOUT: CONVERSION RESULT FROM

PREVIOUSLY SELECTED CHANNEL ADD3 TO

CHANNEL ADD0

ADIN: WRITE TO CONTROL REGISTER,

WRITE BIT = 1,

SELECT CODING, RANGE, AND POWER MODE

SELECT CHANNEL ADD3 TO CHANNEL ADD0

FOR CONVERSION, SEQ = SHADOW = 0

ADIN: WRITE TO CONTROL REGISTER,

WRITE BIT = 1,

SELECT CODING, RANGE, AND POWER MODE

SELECT CHANNEL ADD3 TO CHANNEL ADD0

FOR CONVERSION,

SEQ = SHADOW = 0

DUMMY CONVERSIONS

ADIN = ALL 1s

ASYNC

WRITE BIT = 1,

SEQ = SHADOW = 0

POWER ON

Figure 69. Sequence Function Not Used

DUMMY CONVERSIONS

ADIN = ALL 1s

ADIN: WRITE TO CONTROL REGISTER,

WRITE BIT = 1,

SELECT CODING, RANGE, AND POWER MODE

SELECT CHANNEL ADD3 TO CHANNEL ADD0

FOR CONVERSION, SEQ = 0 SHADOW = 1

ASYNC

ADOUT: CONVERSION RESULT FROM

PREVIOUSLY SELECTED CHANNEL ADD3 TO

CHANNEL ADD0

ADIN: WRITE TO SHADOW REGISTER,

SELECTING WHICH CHANNELS TO CONVERT

ON; CHANNELS SELECTED NEED NOT BE

CONSECUTIVE

POWER ON

CONTINUOUSLY

CONVERTS ON THE

SELECTED SEQUENCE

OF CHANNELS

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 = 0

WRITE

BIT = 0

WRITE BIT = 1,

SEQ = 1, SHADOW = 0

WRITE BIT = 1,

SEQ = 1,

SHADOW = 0

Figure 70. Continuous Conversions

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

DUMMY CONVERSIONS

ADIN = ALL 1s

ADIN: WRITE TO CONTROL REGISTER,

WRITE BIT = 1,

SELECT CODING, RANGE, AND POWER MODE

SELECT CHANNEL ADD3 TO CHANNEL ADD0

FOR CONVERSION, SEQ = 1 SHADOW = 1

ASYNC

ADOUT: CONVERSION RESULT FROM

CHANNEL 0

CONTINUOUSLY CONVERTS ON A

CONSECUTIVE SEQUENCE OF CHANNELS

FROM CHANNEL 0 UP TO AND INCLUDING

THE PREVIOUSLY SELECTED CHANNEL

ADD3 TO CHANNEL ADD0 IN THE CONTROL

WRITE BIT = 1,

SEQ = 1,

SHADOW = 0

POWER ON

WRITE

BIT = 0

WRITE BIT = 1,

SEQ = 1,

SHADOW = 0

Figure 71. Continuous Conversion Without Programming

the Shadow Register

AD5590BBC Datasheet(PDF) 39 Page - Analog Devices

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