ADGS1208BCPZ datasheet(25/33 Pages) AD

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Data Sheet

ADGS1208/ADGS1209

Rev. 0 | Page 25 of 33

ROUND ROBIN MODE

Round robin mode allows the ADGS1208/ADGS1209 to cycle

through the channels faster by reducing the overhead needed

from the digital interface to switch from one channel to the

next. The round robin configuration register selects which

channels are to be included in a cycle, while the CNV edge

select register selects on which edge of CNV the ADGS1208/

ADGS1209 switch to the next channel in the sequence. At the

end of the channel cycle, a resync pulse appears on SDO to

inform the user that the current cycle ended and then it loops

back to the start of the sequence of channels. Figure 52 shows

an example of the round robin mode interface and Figure 53

shows the CNV signal of the analog-to-digital converter (ADC)

being used in conjunction with the ADGS1208 in round robin

mode.

After configuration completes, the round robin enable register

allows the ADGS1208/ADGS1209 to enter round robin mode.

When in round robin mode, the SPI is no longer used to switch

between channels. Instead, to switch from one channel to

another, ensure that a digital signal is present on the CNV pin

while CS is pulled low.

To exit round robin mode, either perform a hardware reset or

send the 16-bit addressable mode SPI frames: 0xA318 followed

by 0xE3B4. These are the only SPI commands recognized by the

SPI interface while in round robin mode.

Round robin mode is significantly faster than addressable mode

to cycle through channels because it removes the 16-bit

overhead required to change input channel. In addition, round

robin mode removes the need for SCLK to be running, which

reduces the digital current consumption (IL). The maximum

CNV frequency is bound by the transition time of the device,

along with the required settling time for the application.

CNV

MUX

CHANNEL

S(LAST)

ROUND ROBIN CYCLE

SDO

RESYNC

Figure 52. Round Robin Mode Interface Example

CNV

AQUISITION

tACQ

tCYC

tCONV

tDIS

tEN

CONVERSION

SCK

SDO

MUX

CHANNEL

D15

D14

N + 2

N + 1

D13

AD7980 SDO

SDI

DATA IN

DIGITAL HOST

CLK

VIO

CNV

SCK

CONVERT

IN0

IN1

IN2

IN7

ADGS1208

SCK

GPO

CNV

Figure 53. Example of CNV Signal of an ADC Cycling Through Channels in the ADGS1208

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