ADS1258IPHPREP datasheet(30/57 Pages) TI

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DRDY

START Pin

Pulse Convert

Command

Converting

Idle

Data Ready, Index to Next Channel

DRDY

STARTPin

SDSU

DRHD

SYMBOL

DESCRIPTION

MIN

UNIT

SDSU

tCLK

DRHD

STARTto

SetupTime

DRDY

toHaltFurtherConversions

DRDY toSTARTHoldTime

toCompleteCurrentConversion

DRDY

START Pin

Data Ready, Index to Next Channel

Idle

Idle Mode

Converting

ADS1258-EP

SBAS445C – MARCH 2009 – REVISED DECEMBER 2009

www.ti.com

Pulse Convert Command

CONVERSION CONTROL

Figure 55 also shows the start of conversions with the

The conversions of the ADS1258 are controlled by

rising edge of the START pin. If the START pin is

the START pin. Conversions begin when the START

taken high, and then low prior to completion of the

pin is taken high and conversions are stopped when

conversion cycle (8

τCLK before DRDY asserts low),

the

START

taken

low.

For

continuous

only the current channel is converted and the device

conversions, tie the START pin high. The START pin

enters the standby or sleep modes waiting for a new

can also be tied low and the conversions controlled

start condition. Figure 56 shows the START pin to

by the PULSE convert command. The PULSE

DRDY timing. The same function of conversion

convert command converts one channel (only) for

control is possible using the Pulse Convert command

each

command

sent.

this

way,

channel

(with the START pin low). In this operation, the data

conversions can be stepped without the need to

from one channel is converted with each Pulse

toggle the START pin.

Convert command. The Pulse convert command

takes effect when the command byte is completely

START Pin

shifted in (eighth falling edge of SCLK). After

As shown in Figure 54, when the START pin is taken

conversion, if more than one channel is enabled

high, conversions start beginning with the current

(Auto-Scan mode), the converter indexes to the next

channel. The device continues to convert all of the

selected channel after completing the conversion.

programmed channels, in a continuous loop, until the

START pin is taken low. When this occurs, the

conversion in process completes, and the device

enters the standby or sleep mode waiting for a new

start

condition.

When

DRDY

asserts

low,

the

conversion data is ready. Figure 56 shows the

START pin to DRDY timing. The order in which

channel data is converted is described in Table 10.

When the last selected channel in the program list

has

been

converted,

the

device

continues

conversions starting with the highest priority channel.

If there is only one channel selected in the Auto-Scan

mode, the converter remains fixed on one channel. A

Figure 55. Pulse Conversion, Auto-Scan Mode

write operation to any of the multiplexer channel

select registers sets the channel pointer to the

highest

priority

channel

(see

Table

11).

Fixed-Channel mode, the channel pointer remains

fixed.

Figure 56. START Pin and DRDY Timing

Figure 54. Conversion Control, Auto-Scan Mode

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