ADS1299
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SBAS499A –JULY 2012–REVISED AUGUST 2012
Data Output (DOUT)
The data output pin (DOUT) is used with SCLK to read conversion and register data from the ADS1299. Data on
DOUT are shifted out on the SCLK rising edge. DOUT goes to a high-impedance state when CS is high. In read
data continuous mode (see the SPI Command Definitions section for more details), the DOUT output line also
indicates when new data are available. This feature can be used to minimize the number of connections between
the device and system controller.
Figure 32 shows the ADS1299 data output protocol.
DRDY
CS
SCLK
216 SCLKs
DOUT
DIN
STAT
CH1
CH2
CH3
CH4
CH5
CH6
CH7
CH8
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
24-Bit
Figure 32. SPI Bus Data Output
Data Retrieval
Data retrieval can be accomplished in one of two methods. The read data continuous command (see the
RDATAC: Read Data Continuous section) can be used to set the device in a mode to read data continuously
without sending opcodes. The read data command (see the RDATA: Read Data section) can be used to read
just one data output from the device (see the SPI Command Definitions section for more details). Conversion
data are read by shifting data out on DOUT. The MSB of the data on DOUT is clocked out on the first SCLK
rising edge. DRDY returns to high on the first SCLK falling edge. DIN should remain low for the entire read
operation.
The number of bits in the data output depends on the number of channels and the number of bits per channel.
For the ADS1299, the number of data outputs is [(24 status bits + 24 bits × 8 channels) = 216 bits]. The format of
the 24 status bits is: (1100 + LOFF_STATP + LOFF_STATN + bits[4:7] of the GPIO register). The data format for
each channel data are twos complement and MSB first. When channels are powered down using the user
register setting, the corresponding channel output is set to '0'. However, the channel output sequence remains
the same.
The ADS1299 also provides a multiple readback feature. Data can be read out multiple times by simply giving
more SCLKs, in which case the MSB data byte repeats after reading the last byte. The DAISY_EN bit in the
CONFIG1 register must be set to '1' for multiple readbacks.
Data Ready (DRDY)
DRDY is an output. When DRDY transitions low, new conversion data are ready. The CS signal has no effect on
the data ready signal. DRDY behavior is determined by whether the device is in RDATAC mode or the RDATA
command is used to read data on demand. (See the RDATAC: Read Data Continuous and RDATA: Read Data
subsections of the SPI Command Definitions section for further details).
When reading data with the RDATA command, the read operation can overlap the next DRDY occurrence
without data corruption.
The START pin or the START command places the device either in normal data capture mode or pulse data
capture mode.
Copyright © 2012, Texas Instruments Incorporated
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