ST24LC21B1TR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
ST24LC21B1TR Datasheet PDF : 18 Pages
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ST24LC21
SIGNAL DESCRIPTIONS
I2C Serial Clock (SCL). The SCL input pin is used
to synchronize all data in and out of the memory. A
resistor can be connected from the SCL line to VCC
to act as a pull up (see Figure 5).
Transmit Only Clock (VCLK). The VCLK input pin
is used to synchronize data out when the
ST24LC21 is in Transmit Only mode. The VCLK
input offers also a Write Enable (active high) func-
tion when the ST24LC21 is in I2C bidirectional
mode.
Serial Data (SDA). The SDA pin is bi-directional
and is used to transfer data in or out of the memory.
It is an open drain output that may be wire-OR’ed
with other open drain or open collector signals on
the bus. A resistor must be connected from the SDA
bus line to VCC to act as pull up (see Figure 5).
DEVICE OPERATION
I2C Bus Background
The ST24LC21 supports the I2C protocol. This
protocol defines any device that sends data onto
the bus as a transmitter and any device that reads
the data as a receiver. The device that controls the
data transfer is known as the master and the other
as the slave. The master will always initiate a data
transfer and will provide the serial clock for syn-
chronisation. The ST24LC21 are always slave de-
vices in all communications.
Start Condition. START is identified by a high to
low transition of the SDA line while the clock SCL
is stable in the high state. A START condition must
precede any command for data transfer. Except
during a programming cycle, the ST24LC21 con-
tinuously monitor the SDA and SCL signals for a
START condition and will not respond unless one
is given.
Stop Condition. STOP is identified by a low to high
transition of the SDA line while the clock SCL is
stable in the high state. A STOP condition termi-
nates communication between the ST24LC21 and
the bus master. A STOP condition at the end of a
Read command forces the standby state. A STOP
condition at the end of a Write command triggers
the internal EEPROM write cycle.
Acknowledge Bit (ACK). An acknowledge signal
is used to indicate a successfull data transfer. The
bus transmitter, either master or slave, will release
the SDA bus after sending 8 bits of data. During the
9th clock pulse period the receiver pulls the SDA
bus low to acknowledge the receipt of the 8 bits of
data.
Figure 5. Maximum RL Value versus Bus Capacitance (CBUS) for an I2C Bus
20
16
12
8
4
0
10
VCC
fc = 100kHz
fc = 400kHz
100
CBUS (pF)
RL
SDA
MASTER
SCL
RL
CBUS
1000
CBUS
AI01665
5/18
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