M24128, M24C64, M24C32
Device operation
4.5
Memory addressing
To start communication between the bus master and the slave device, the bus master must
initiate a Start condition. Following this, the bus master sends the device select code, shown
in
(on Serial Data (SDA), most significant bit first).
The device select code consists of a 4-bit device type identifier, and a 3-bit Chip Enable
“Address” (E2, E1, E0). To address the memory array, the 4-bit device type identifier is
1010b.
Up to eight memory devices can be connected on a single I
2
C bus. Each one is given a
unique 3-bit code on the Chip Enable (E0, E1, E2) inputs. When the device select code is
received, the device only responds if the Chip Enable Address is the same as the value on
the Chip Enable (E0, E1, E2) inputs.
The 8
th
bit is the Read/Write bit (RW). This bit is set to 1 for Read and 0 for Write operations.
If a match occurs on the device select code, the corresponding device gives an
acknowledgment on Serial Data (SDA) during the 9
th
bit time. If the device does not match
the device select code, it deselects itself from the bus, and goes into Standby mode.
Table 6.
Mode
Current Address
Read
Random Address
Read
Sequential Read
Byte Write
Operating modes
RW bit WC
(1)
1
0
1
1
0
X
X
1
X
X
V
IL
V
IL
≥
1
1
≤
32 for M24C64
and M24C32
≤
64 for M24128
reStart, device select, RW = 1
Similar to Current or Random Address
Read
Start, device select, RW = 0
Bytes
1
Initial sequence
Start, device select, RW = 1
Start, device select, RW = 0, Address
Page Write
0
Start, device select, RW = 0
1. X =
V
IH
or V
IL
.
13/35
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