Datasheet

1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8 1 2 3 4 5 6 7 8
NOTES: (1)OptionalforAuto-Scanmode,disabledforFixed-Channelmode.SeeTable13,StatusByte.
(2)Afterthechanneldatareadoperation, mustbetoggledoranSPItimeoutmustoccurbeforesendingcommands.
(3)NoSCLKactivity.
CS
(3)
DRDY
CS
SCLK
DOUT
DIN
(holdinactive)
StatusByte
(1)
DataByte1(MSB) DataByte3(MSB)
(2)
ADS1258
SBAS297G –JUNE 2005– REVISED MARCH 2011 www.ti.com
write operations in progress will terminate and the may be read at any time without concern to DRDY.
SPI interface resets. This timeout feature can be The NEW bit of the STATUS byte indicates that the
used to recover lost communication when a serial data register has been refreshed with new converter
interface transmission is interrupted or inadvertently data since the last read operation. The data is shifted
glitched. out MSB first after the STATUS byte.
It should be noted that on system power-up, if the
Data Input (DIN) and Data Output (DOUT)
ADS1258 interface signals are floating or undefined,
Operation
the interface could wake in an unknown state. This
The data input pin (DIN) is used to input data to the
condition is remedied by resetting the interface in
ADS1258. The data output pin (DOUT) is used to
three ways: toggle the RESET pin low then high;
output data from the ADS1258. Data on DIN is shifted
toggle the CS pin high then low; or hold SCLK
into the converter on the rising edge of SCLK while
inactive for 2
18
+ 4096 f
CLK
cycles.
data is shifted out on DOUT on the falling edge of
SCLK. DOUT is tri-stated when CS is high to allow
Channel Data Read Direct
multiple devices to share the line.
Channel data can be accessed from the ADS1258 in
two ways: Direct data read or data read with register
SPI Bus Sharing
format. With Direct read, the DIN input pin is held
The ADS1258 can be connected to a shared SPI bus.
inactive (high or low) for at least the first three SCLK
DOUT tri-states when CS is deselected (high). When
transitions. When the first three bits are 000 or 111,
the ADS1258 is connected to a shared bus, data can
the device detects a direct data read and continues to
be read only by the Channel Data Read command
output conversion data. After the device defects this
format.
read format, commands are ignored until either CS is
toggled, an SPI timeout occurs or the device is reset.
COMMUNICATION PROTOCOL The Channel Data Read command does not have
this requirement.
Communicating to the ADS1258 involves shifting data
into the device (via the DIN pin) or shifting data out of Concurrent with the first SCLK transition, channel
the device (via the DOUT pin) under control of the data is output on the DOUT output pin. A total of 24
SCLK input. or 32 SCLK transitions complete the data read
operation. The number of shifts depend on whether
Reading DATA the status byte is enabled. The data must be
completely shifted out before the next occurrence of
DRDY goes low to indicate that data for one channel
DRDY or the remaining data will be corrupted. It is
are ready. The channel data may be read via a direct
recommended to monitor DRDY to synchronize the
data read (Channel Data Read Direct) or the data
start of the read operation to avoid data corruption.
may be read in a register format (Channel Data Read
Before DRDY asserts low, the MSB of the Status byte
Register). A direct data read requires the data to be
or the MSB of the data is output on DOUT (CS = '0'),
read before the next occurrence of DRDY or the data
as shown in Figure 57. In this format, reading the
for that channel are overwritten with new data from
data a second time within the same DRDY frame
the next channel. This type of data read requires
returns data = 0.
synchronization with DRDY to avoid this conflict.
When reading data in the register format, the data
Figure 57. Channel Data Read Direct (No Command)
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