Mode RW bit MODE Bytes Initial Sequence
Current Address Read ’1’ X 1 START, Device Select, R
W = ’1’
Random Address Read
’0’
X1
START, Device Select, R
W = ’0’, Address,
’1’ reSTART, Device Select, R
W = ’1’
Sequential Read ’1’ X 1 to 1024 Similar to Current or Random Mode
Byte Write ’0’ X 1 START, Device Select, R
W = ’0’
Multibyte Write
(2)
’0’ V
IH
8 START, Device Select, RW = ’0’
Page Write ’0’ V
IL
16 START, Device Select, RW = ’0’
Notes:
1. X = V
IH
or V
IL
2. Multibyte Write not available in ST24/25W08 versions.
Table 4. Operating Modes
(1)
Device Code
Chip
Enable
Block
Select
R
W
Bit b7 b6 b5 b4 b3 b2 b1 b0
Device Select 1 0 1 0 E A9 A8 R
W
Note:
The MSB b7 is sent first.
Table 3. Device Select Code
When writing data to the memory it responds to the
8 bits received by asserting an acknowledge bit
during the 9th bit time. When data is read by the
bus master, it acknowledges the receipt of the data
bytes in the same way. Data transfers are termi-
nated with a STOP condition.
Power On Reset: V
CC
lock out write protect. In
order to prevent data corruption and inadvertent
write operations during power up, a Power On
Reset (POR) circuit is implemented. Until the V
CC
voltage has reached the POR threshold value, the
internal reset is active, all operations are disabled
and the device will not respond to any command.
In the same way, when V
CC
drops down from the
operating voltage to below the POR threshold
value, all operations are disabled and the device
will not respond to any command. A stable V
CC
must be applied before applying any logic signal.
SIGNAL DESCRIPTIONS
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 V
CC
to act as a pull up (see Figure 3).
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 V
CC
to act as pull up (see Figure 3).
Chip Enable (E). This chip enable input is used to
set one least significant bit (b3) of the device select
byte code. This input may be driven dynamically or
tied to V
CC
or V
SS
to establish the device select
code.
Protect Enable (PRE). The PRE input pin, in ad-
dition to the status of the Block Address Pointer bit
(b2, location 3FFh as in Figure 7), sets the PRE
write protection active.
Mode (MODE). The MODE input is available on pin
7 (see also
WC feature) and may be driven dynami-
cally. It must be at V
IL
or V
IH
for the Byte Write
mode, V
IH
for Multibyte Write mode or V
IL
for Page
Write mode. When unconnected, the MODE input
is internally read as a V
IH
(Multibyte Write mode).
Write Control (
WC). An hardware Write Control
(
WC) feature is offered only for ST24W08 and
ST25W08 versions on pin 7. This feature is usefull
to protect the contents of the memory from any
erroneous erase/write cycle. The Write Control sig-
nal is used to enable (
WC = V
IH
) or disable (WC =
V
IL
) the internal write protection. When uncon-
nected, the
WC input is internally read as V
IL
and
the memory area is not write protected.
3/16
ST24/25C08, ST24/25W08
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