Datasheet

DRDY
START Pin
Pulse Convert
Command
Converting ConvertingIdle
Data Ready, Index to Next Channel
or
DRDY
STARTPin
t
SDSU
t
DRHD
SYMBOL DESCRIPTION MIN UNIT
t
SDSU
8
t
CLK
8
t
CLK
t
DRHD
STARTto SetupTime
DRDY
toHaltFurtherConversions
DRDY toSTARTHoldTime
toCompleteCurrentConversion
DRDY
START Pin
Data Ready, Index to Next Channel
IdleIdle Mode Converting
ADS1258-EP
SBAS445D –MARCH 2009– REVISED MARCH 2011 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 τ
CLK
before DRDY asserts low),
the START pin is 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. In 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). In
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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