MAX11040 datasheet(22/31 Pages) MAXIM

22 / 31 page

24-Bit, 4-Channel, Simultaneous-Sampling,

Cascadable, Sigma-Delta ADC

______________________________________________________________________________________

Multiple Device Connection

Daisy chain up to eight MAX11040 devices for applica-

tions that require up to 32 simultaneously sampled inputs

over a single SPI-/DSP-compatible serial interface with a

single chip-select signal, and single interface commands

that apply to all devices in the chain. The eight

MAX11040 devices effectively operate as one device.

There are two aspects to cascading multiple devices:

the digital interface and the mechanism for keeping

multiple devices sampling simultaneously.

There are many configurations for connecting multiple

devices; one is described in the next section, others

are described in the

Synchronizing Multiple Devices

section within the

Applications Information section.

Multiple Device Digital Interface

Figure 12 shows the most common way to daisy chain

the digital interface of multiple devices.

SPI bus arbitration is performed using CASCIN and

CASCOUT. A falling edge at the CASCIN input of device

n, which is driven by the CASCOUT of device n-1,

allows device n to take over the SPI bus until all expect-

ed data is written or read; at this point, device n pulls its

CASCOUT output low. Similarly, CASCOUT of device n

drives CASCIN of device n+1. Figures 11 and 13 show

read operations, including CASCIN and CASCOUT tim-

ings, for two cascaded devices and eight cascaded

devices, respectively. The operation described above

applies to all register operations except for writes to the

Data Rate Control register. A fixed 16-bit word is written

to the Data Rate Control registers of all devices in the

chain, independent of the number of cascaded devices

(see Figure 14). Reading from the Data Rate Control

Connecting the open-drain OVRFLW output of all

devices together creates one signal that summarizes

the overflow information of all devices. This is also true

of the FAULT output. Connecting together these out-

puts from multiple devices has the effect of a “wire

NOR.” Any device that has an active condition on these

outputs is allowed to pull the line low.

MAX11040

SYNC

SCLK

DIN

CASCIN

DRDYIN

DRDYOUT

FAULT

OVRFLW

DOUT

XIN

DEVICE n+1

DEVICE 0

DEVICE n

MAX11040

SYNC

SCLK

DIN

CASCIN

DRDYIN

CASCOUT

FAULT

OVRFLW

DOUT

XIN

XOUT CLKOUT

MAX11040

SYNC

SCLK

DIN

CASCIN

DRDYIN

CASCOUT

FAULT

OVRFLW

DOUT

XIN

DSP OR

MICROCONTROLLER

CASCADE UP TO 8 DEVICES

Figure 12. Daisy Chaining Multiple Devices

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