ST24/25C16, ST24/25W16
Figure 7. Memory Protection
PB1
Block
Select
1
PB0
Protect Location
16 byte
boundary
address
b7
7FFh
700h
Block 6
600h
Block 5
500h
Block 4
400h
0
0
0
1
1
0
b4
0
Protect Flag
Enable = 0
Disable = 1
b2
X
X
Block 7
1
1
PB1 PB0
AI00870B
Write Operations
The Multibyte Write mode (only available on the
ST24/25C16 versions) is selected when the MODE
pin is at V
IH
and the Page Write mode when MODE
pin is at V
IL
. The MODE pin may be driven dynami-
cally with CMOS input levels.
Following a START condition the master sends a
device select code with the RW bit reset to ’0’. The
memory acknowledges this and waits for a byte
address. The byte address of 8 bits provides ac-
cess to any of the 256 bytes of one memory block.
After receipt of the byte address the device again
responds with an acknowledge.
For the ST24/25W16 versions, any write command
with WC = ’1’ (during a period of time from the
START condition untill the end of the Byte Address)
will not modify data and will NOT be acknowledged
on data bytes, as in Figure 10.
Byte Write.
In the Byte Write mode the master
sends one data byte, which is acknowledged by the
memory. The master then terminates the transfer
by generating a STOP condition. The Write mode
is independant of the state of the MODE pin which
could be left floating if only this mode was to be
used. However it is not a recommended operating
mode, as this pin has to be connected to either V
IH
or V
IL
, to minimize the stand-by current.
Multibyte Write (ST24/25C16 only).
For the Mul-
tibyte Write mode, the MODE pin must be at V
IH
.
The Multibyte Write mode can be started from any
address in the memory. The master sends from one
up to 8 bytes of data, which are each acknowledged
by the memory. The transfer is terminated by the
master generating a STOP condition. The duration
of the write cycle is t
W
= 10ms maximum except
when bytes are accessed on 2 contiguous rows
(one row is 16 bytes), the programming time is then
doubled to a maximum of 20ms. Writing more than
8 bytes in the Multibyte Write mode may modify
data bytes in an adjacent row (one row is 16 bytes
long). However, the Multibyte Write can properly
write up to 16 consecutive bytes only if the first
address of these 16 bytes is the first address of the
row, the 15 following bytes being written in the 15
following bytes of this same row.
9/17
STMICROELECTRONICS [ STMICROELECTRONICS ]
