Datasheet

ADS1113
ADS1114
ADS1115
SBAS444B –MAY 2009–REVISED OCTOBER 2009 www.ti.com
SMBus ALERT RESPONSE An I
2
C bus consists of two lines, SDA and SCL. SDA
carries data; SCL provides the clock. All data are
When configured in latching mode (COMP_LAT = '1'
transmitted across the I
2
C bus in groups of eight bits.
in the Config register), the ALERT/RDY pin can be
To send a bit on the I
2
C bus, the SDA line is driven to
implemented with an SMBus alert. The pin asserts if
the appropriate level while SCL is low (a low on SDA
the comparator detects a conversion that exceeds an
indicates the bit is zero; a high indicates the bit is
upper or lower threshold. This interrupt is latched and
one). Once the SDA line settles, the SCL line is
can be cleared only by reading conversion data, or by
brought high, then low. This pulse on SCL clocks the
issuing a successful SMBus alert response and
SDA bit into the receiver shift register. If the I
2
C bus
reading the asserting device I
2
C address. If
is held idle for more than 25ms, the bus times out.
conversion data exceed the upper or lower thresholds
after being cleared, the pin reasserts. This assertion The I
2
C bus is bidirectional: the SDA line is used for
does not affect conversions that are already in both transmitting and receiving data. When the
progress. The ALERT/RDY pin, as with the SDA pin, master reads from a slave, the slave drives the data
is an open-drain pin. This architecture allows several line; when the master sends to a slave, the master
devices to share the same interface bus. When drives the data line. The master always drives the
disabled, the pin holds a high state so that it does not clock line. The ADS1113/4/5 never drive SCL,
interfere with other devices on the same bus line. because they cannot act as a master. On the
ADS1113/4/5, SCL is an input only.
When the master senses that the ALERT/RDY pin
has latched, it issues an SMBus alert command Most of the time the bus is idle; no communication
(00011001) to the I
2
C bus. Any ADS1114/5 data occurs, and both lines are high. When communication
converters on the I
2
C bus with the ALERT/RDY pins is taking place, the bus is active. Only master devices
asserted respond to the command with the slave can start a communication and initiate a START
address. In the event that two or more ADS1114/5 condition on the bus. Normally, the data line is only
data converters present on the bus assert the latched allowed to change state while the clock line is low. If
ALERT/RDY pin, arbitration during the address the data line changes state while the clock line is
response portion of the SMBus alert decides which high, it is either a START condition or a STOP
device clears its assertion. The device with the lowest condition. A START condition occurs when the clock
I
2
C address always wins arbitration. If a device loses line is high and the data line goes from high to low. A
arbitration, it does not clear the comparator output pin STOP condition occurs when the clock line is high
assertion. The master then repeats the SMBus alert and the data line goes from low to high.
response until all devices have had the respective
After the master issues a START condition, it sends a
assertions cleared. In window comparator mode, the
byte that indicates which slave device it wants to
SMBus alert status bit indicates a '1' if signals exceed
communicate with. This byte is called the address
the high threshold and a '0' if signals exceed the low
byte. Each device on an I
2
C bus has a unique 7-bit
threshold.
address to which it responds. The master sends an
address in the address byte, together with a bit that
I
2
C INTERFACE
indicates whether it wishes to read from or write to
the slave device.
The ADS1113/4/5 communicate through an I
2
C
interface. I
2
C is a two-wire open-drain interface that
Every byte transmitted on the I
2
C bus, whether it is
supports multiple devices and masters on a single
address or data, is acknowledged with an
bus. Devices on the I
2
C bus only drive the bus lines
acknowledge bit. When the master has finished
low by connecting them to ground; they never drive
sending a byte (eight data bits) to a slave, it stops
the bus lines high. Instead, the bus wires are pulled
driving SDA and waits for the slave to acknowledge
high by pull-up resistors, so the bus wires are high
the byte. The slave acknowledges the byte by pulling
when no device is driving them low. This way, two
SDA low. The master then sends a clock pulse to
devices cannot conflict; if two devices drive the bus
clock the acknowledge bit. Similarly, when the master
simultaneously, there is no driver contention.
has finished reading a byte, it pulls SDA low to
acknowledge this to the slave. It then sends a clock
Communication on the I
2
C bus always takes place
pulse to clock the bit. (The master always drives the
between two devices, one acting as the master and
clock line.)
the other as the slave. Both masters and slaves can
read and write, but slaves can only do so under the
A not-acknowledge is performed by simply leaving
direction of the master. Some I
2
C devices can act as
SDA high during an acknowledge cycle. If a device is
masters or slaves, but the ADS1113/4/5 can only act
not present on the bus, and the master attempts to
as slave devices.
address it, it receives a not-acknowledge because no
device is present at that address to pull the line low.
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