ADS1258IPHPREP datasheet(31/57 Pages) TI

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Initial Delay

Fully−Settled Data

DRDY

Start

Condition

ADS1258-EP

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SBAS445C – MARCH 2009 – REVISED DECEMBER 2009

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

the converter automatically measures and sequences

through the channels either in a continuous loop or

pulse-step

fashion,

depending

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)

(fCLK cycles)

DRATE[1:0]

Fixed-Channel

Auto-Scan

Fixed-Channel

Auto-Scan

802

708

866

772

1186

1092

1250

1156

2722

2628

2786

2692

8866

8772

8930

8836

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ADS1258IPHPREP Datasheet(PDF) 31 Page - Texas Instruments

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