LTC2487
applicaTions inForMaTion
I C INTERFACE
2
finished, aStop(P)conditionisgeneratedbytransitioning
SDA from low to high while SCL is high. The bus is free
after a Stop is generated. Start and Stop conditions are
always generated by the master.
2
TheLTC2487communicatesthroughanI Cinterface. The
2
I C interface is a 2-wire, open-drain interface supporting
multipledevicesandmultiplemastersonasinglebus. The
connected devices can only pull the data line (SDA) low
andcanneverdriveithigh. SDAisrequiredtobeexternally
connected to the supply through a pull-up resistor. When
the data line is not being driven, it is high. Data on the
When the bus is in use, it stays busy if a Repeated Start
(Sr)isgeneratedinsteadofaStopcondition. Therepeated
Start timing is functionally identical to the Start and is
used for writing and reading from the device before the
initiation of a new conversion.
2
I C bus can be transferred at rates up to 100kbits/s in the
standard mode and up to 400kbits/s in the fast mode.
Data Transferring
2
Each device on the I C bus is recognized by a unique
2
address stored in that device and can operate either as a
transmitter or receiver, depending on the function of the
device. In addition to transmitters and receivers, devices
canalsobeconsideredasmastersorslaveswhenperform-
ing data transfers. A master is the device which initiates a
data transfer on the bus and generates the clock signals
to permit that transfer. Devices addressed by the master
are considered a slave.
After the Start condition, the I C bus is busy and data
transfer can begin between the master and the addressed
slave. Data is transferred over the bus in groups of nine
bits, one byte followed by one acknowledge (ACK) bit.
The master releases the SDA line during the ninth SCL
clock cycle. The slave device can issue an ACK by pulling
SDA low or issue a Not Acknowledge (NAK) by leaving
the SDA line high impedance (the external pull-up resistor
will hold the line high). Change of data only occurs while
the clock line (SCL) is low.
The LTC2487 can only be addressed as a slave. Once ad-
dressed, it can receive configuration bits (channel selec-
tion, rejection mode, speed mode, gain) or transmit the
last conversion result. The serial clock line, SCL, is always
an input to the LTC2487 and the serial data line SDA is
bidirectional. The device supports the standard mode and
the fast mode for data transfer speeds up to 400kbits/s.
DATA FORMAT
After a Start condition, the master sends a 7-bit address
followed by a read/write (R/W) bit. The R/W bit is 1 for
a read request and 0 for a write request. If the 7-bit ad-
dress matches the hard wired LTC2487’s address (one of
9 pin-selectable addresses) the device is selected. When
the device is addressed during the conversion state, it will
not acknowledge R/W requests and will issue a NAK by
leaving the SDA line high. If the conversion is complete,
the LTC2487 issues an ACK by pulling the SDA line low.
2
Figure 2 shows the definition of the I C timing.
The Start and Stop Conditions
AStart(S)conditionisgeneratedbytransitioningSDAfrom
high to low while SCL is high. The bus is considered to be
busy after the Start condition. When the data transfer is
SDA
t
SU(DAT)
t
t
t
t
BUF
t
t
t
t
r
LOW
HD(SDA)
SP
f
r
f
SCL
t
t
t
SU(STO)
HD(SDA)
SU(STA)
t
t
HIGH
S
Sr
P
S
HD(DAT)
2487 F02
2
Figure 2. Definition of Timing for Fast/Standard Mode Devices on the I C Bus
2487fa
ꢀꢃ
Linear [ Linear ]
