MAX11040_10 Datasheet, PDF (22/32 Pages) Maxim Integrated Products – 24-Bit, 4-Channel, Simultaneous-Sampling,Cascadable,Sigma-Delta ADC

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
register returns 16 bits per cascaded device.
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.
DSP OR
MICROCONTROLLER
SYNC
CS
SCLK
DIN
MAX11040
CASCIN
CASCOUT
DRDYIN
DEVICE 0
FAULT
OVRFLW
DOUT
XIN XOUT CLKOUT
SYNC
CS
SCLK
DIN
MAX11040
CASCIN
CASCOUT
DRDYIN
DEVICE n
FAULT
OVRFLW
DOUT
XIN
SYNC
CS
SCLK
DIN
MAX11040
CASCIN
DRDYOUT
DRDYIN
DEVICE n+1
FAULT
OVRFLW
DOUT
XIN
CASCADE UP TO 8 DEVICES
Figure 12. Daisy Chaining Multiple Devices
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