Datasheet

Initial Delay
Fully−Settled Data
DRDY
Start
Condition
ADS1258-EP
www.ti.com SBAS445D –MARCH 2009– REVISED MARCH 2011
GPIO Linked START Pin Control
OPERATING MODES
The START pin can be contolled directly by software
The operating modes of the ADS1258 are defined in
by connecting externally a GPIO port pin to the
three basic states: Converting Mode, Idle Mode, and
START pin. (Note that an external pull-down resistor
Power-Down mode. In Converting mode, the device
is recommended to keep the GPIO from floating until
is actively converting channel data. The device power
the GPIO is configured as an output). For this mode
dissipation is the highest in this mode. This mode is
of control, the START pin is effectively controlled by
divided into two sub-modes: Auto-Scan and
writing to the GPIO Data Register (GPIOD), with the
Fixed-Channel.
write operation setting or resetting the appropriate bit.
The next mode is the Idle mode. In this mode, the
The data takes effect on the eighth falling edge of the
device is not converting channel data. The device
data byte write. The START pin can then be
remains active, waiting for input to start conversions.
controlled by the serial interface.
The power consumption is reduced from that of the
Converting mode. This mode also has two
Initial Delay
sub-modes: Standby and Sleep.
As seen in Figure 57, when a start convert condition
The last mode is Power-Down mode. In this mode, all
occurs, the first reading from ADS1258 is delayed for
functions of the converter are disabled to reduce
a number of clock cycles. This delay allows fully
power consumption to a minimum.
settled data to occur at the first data read. Data reads
thereafter are available at the full data rate. The
CONVERTING MODES
number of clock cycles delayed before the first
reading is valid depends on the data rate setting, and
The ADS1258 has two converting modes: Auto-Scan
whether exiting the Standby or Sleep Mode. Table 9
and Fixed-Channel. In Auto-Scan mode, the channels
lists the delayed clock cycles versus data rate.
to be measured are pre-selected in the address
register settings. When a convert condition is present,
the converter automatically measures and sequences
through the channels either in a continuous loop or
pulse-step fashion, depending on the trigger
condition.
In Fixed-Channel mode, the channel address is
selected in the address register settings prior to
acquiring channel data. When a convert condition is
present, the device converts a single channel, either
continuously or in pulse-step fashion, depending on
the trigger condition. The data rate in this mode is
higher than in Auto-Scan Mode since the input
Figure 57. Start Condition to First Data
channels are not indexed for each reading.
The selection of converting modes is set with bit
MUXMOD of register CONFIG0.
Table 9. Start Condition to DRDY Delay, Chop = 0, DLY[2:0] = 000
INITIAL DELAY (Standby Mode) INITIAL DELAY (Sleep Mode)
(f
CLK
cycles) (f
CLK
cycles)
DRATE[1:0] Fixed-Channel Auto-Scan Fixed-Channel Auto-Scan
11 802 708 866 772
10 1186 1092 1250 1156
01 2722 2628 2786 2692
00 8866 8772 8930 8836
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