ADS8555_16 Datasheet, PDF (26/43 Pages) Texas Instruments – 16-Bit, Six-Channel, Simultaneous Sampling Analog-to-Digital Converter

ADS8555
SBAS531D – DECEMBER 2010 – REVISED FEBRUARY 2016
www.ti.com
Device Functional Modes (continued)
If the serial interface is used, input data containing control register contents are required with each read access
to the device in this mode (combined read/write access). For initialization purposes, all 32 bits of the register
must be set (bit C16 must be set to 1 during that access to allow the update of the entire register content). To
minimize switching noise on the interface, an update of the first eight bits (C[31:24]) with the remaining bits held
low can be performed thereafter.
Figure 35 illustrates the different control register update options.
7.4.3 Daisy-Chain Mode (In Serial Mode Only)
The serial interface of the ADS8555 device supports a daisy-chain feature that allows cascading of multiple
devices to minimize the board space requirements and simplify routing of the data and control lines. In this case,
pins DB5/DCIN_A, DB4/DCIN_B, and DB3/DCIN_C are used as serial data inputs for channels A, B, and C,
respectively. Figure 32 shows an example of a daisy-chain connection of three devices sharing a common
CONVST line to allow simultaneous sampling of 18 analog channels along with the corresponding timing
diagram. To activate the daisy-chain mode, the DC_EN pin must be pulled high. As a result of the time
specifications t_S1, t_H1, and t_D3, the maximum SCLK frequency that may be used in daisy-chain mode is 27.78
MHz (assuming 50% duty cycle).
CONVST
FS
SCLK
ADS8555
#1
ADS8555
#2
ADS8555
#3
CONVST_A
FS
SCLK
SDO_A
SDO_B
SDO_C
DC_EN = ‘0’
CONVST_A
FS
SCLK
DCIN_A
DCIN_B
DCIN_C
SDO_A
SDO_B
SDO_C
DC_EN = ‘1’
CONVST_A
FS
SCLK
DCIN_A
DCIN_B
DCIN_C
SDO_A
SDO_B
SDO_C
DC_EN = ‘1’
To
Processing
Unit
CONVST
BUSY
(C20 = C21 = 0)
FS
SDO_x #3
Don’t Care
16-Bit Data CHx0
ADS8555 #3
16-Bit Data CHx1 16-Bit Data CHx0
ADS8555 #3
ADS8555 #2
16-Bit Data CHx1
ADS8555 #2
16-Bit Data CHx0
ADS8555 #1
16-Bit Data CHx1
ADS8555 #1
Figure 32. Example of Daisy-Chaining Three ADS8555 Devices
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