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M24256-AWMN6T View Datasheet(PDF) - STMicroelectronics

Part Name
Description
MFG CO.
'M24256-AWMN6T' PDF : 20 Pages View PDF
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M24256-A
These memory devices are compatible with the
I2C extended memory standard. This is a two wire
serial interface that uses a bi-directional data bus
and serial clock. The memory carries a built-in 4-
bit unique Device Type Identifier code (1010) in
accordance with the I2C bus definition.
The memory behaves as a slave device in the I2C
protocol, with all memory operations synchronized
by the serial clock. Read and Write operations are
initiated by a START condition, generated by the
bus master. The START condition is followed by a
Device Select Code and RW bit (as described in
Table 3), terminated by an acknowledge bit.
When writing data to the memory, the memory in-
serts an acknowledge bit during the 9th bit time,
following the bus master’s 8-bit transmission.
When data is read by the bus master, the bus
master acknowledges the receipt of the data byte
in the same way. Data transfers are terminated by
a STOP condition after an Ack for WRITE, and af-
ter a NoAck for READ.
Power On Reset: VCC Lock-Out Write Protect
In order to prevent data corruption and inadvertent
write operations during power up, a Power On Re-
set (POR) circuit is included. The internal reset is
held active until the VCC voltage has reached the
POR threshold value, and all operations are dis-
abled – the device will not respond to any com-
mand. In the same way, when VCC drops from the
operating voltage, below the POR threshold value,
all operations are disabled and the device will not
respond to any command. A stable and valid VCC
must be applied before applying any logic signal.
SIGNAL DESCRIPTION
Serial Clock (SCL)
The SCL input pin is used to strobe all data in and
out of the memory. In applications where this line
is used by slaves to synchronize the bus to a slow-
er clock, the master must have an open drain out-
put, and a pull-up resistor must be connected from
the SCL line to VCC. (Figure 3 indicates how the
value of the pull-up resistor can be calculated). In
most applications, though, this method of synchro-
nization is not employed, and so the pull-up resis-
tor is not necessary, provided that the master has
a push-pull (rather than open drain) output.
Serial Data (SDA)
The SDA pin is bi-directional, and is used to trans-
fer 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 pull
up resistor must be connected from the SDA bus
to VCC. (Figure 3 indicates how the value of the
pull-up resistor can be calculated).
Chip Enable (E1, E0)
These chip enable inputs are used to set the value
that is to be looked for on the two least significant
bits (b2, b1) of the 7-bit device select code. These
inputs must be tied to VCC or VSS to establish the
device select code. When unconnected, the E1
and E0 inputs are internally read as VIL (see Table
7 and Table 8)
Write Control (WC)
The hardware Write Control pin (WC) is useful for
protecting the entire contents of the memory from
inadvertent erase/write. The Write Control signal is
used to enable (WC=VIL) or disable (WC=VIH)
write instructions to the entire memory area. When
Figure 3. Maximum RL Value versus Bus Capacitance (CBUS) for an I2C Bus
VCC
20
16
12
8
4
0
10
fc = 100kHz
fc = 400kHz
100
CBUS (pF)
RL
SDA
MASTER
SCL
RL
CBUS
1000
CBUS
AI01665
3/20
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