ADS1291_14 Datasheet, PDF (33/75 Pages) Texas Instruments – Power, 2-Channel, 24-Bit Analog Front-End for Biopotential Measurements

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ADS1291
ADS1292
ADS1292R
SBAS502B – DECEMBER 2011 – REVISED SEPTEMBER 2012
Single-Shot Mode
The single-shot mode is enabled by setting the SINGLE_SHOT bit in the CONFIG1 register to '1'. In single-shot
mode, the ADS1291, ADS1292, and ADS1292R perform a single conversion when the START pin is taken high
or when the START opcode command is sent. As seen in Figure 39, when a conversion is complete, DRDY goes
low and further conversions are stopped. Regardless of whether the conversion data are read or not, DRDY
remains low. To begin a new conversion, take the START pin low and then back high, or transmit the START
opcode again. When switching from continuous mode to pulse mode, make sure the START signal is pulsed or
issue a STOP command followed by a START command.
This conversion mode is provided for applications that require non-standard or non-continuous data rates.
Issuing a START command or toggling the START pin high resets the digital filter, effectively dropping the data
rate by a factor of four. Note that this mode leaves the system more susceptible to aliasing effects, requiring
more complex analog anti-aliasing filters at the inputs. Loading on the host processor increases because it must
toggle the START pin or send a START command to initiate a new conversion cycle.
START
t_SETTLE
4 / f_CLK
Data Updating
4 / f_CLK
DRDY
Figure 40. DRDY with No Data Retrieval in Single-Shot Mode
MULTIPLE DEVICE CONFIGURATION
The ADS1291, ADS1292, and ADS1292R are designed to provide configuration flexibility when multiple devices
are used in a system. The serial interface typically needs four signals: DIN, DOUT, SCLK, and CS. With one
additional chip select signal per device, multiple devices can be connected together. The number of signals
needed to interface n devices is 3 + n.
The right leg drive amplifiers can be daisy-chained as explained in the RLD Configuration with Multiple Devices
subsection of the ECG-Specific Functions section. To use the internal oscillator in a daisy-chain configuration,
one of the devices must be set as the master for the clock source with the internal oscillator enabled (CLKSEL
pin = 1) and the internal oscillator clock brought out of the device by setting the CLK_EN register bit to '1'. This
master device clock is used as the external clock source for the other devices.
Copyright © 2011–2012, Texas Instruments Incorporated
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