24AA025E48 Datasheet, PDF (11/28 Pages) Microchip Technology – 2K I2C™ Serial EEPROMs with EUI-48™ Node Identity

24AA02E48/24AA025E48
8.0 READ OPERATION
Read operations are initiated in the same way as write
operations, with the exception that the R/W bit of the
slave address is set to ‘1’. There are three basic types
of read operations: current address read, random read
and sequential read.
8.1 Current Address Read
The 24AAXXXE48 contains an address counter that
maintains the address of the last word accessed, inter-
nally incremented by ‘1’. Therefore, if the previous
access (either a read or write operation) was to address
n, the next current address read operation would
access data from address n + 1. Upon receipt of the
slave address with R/W bit set to ‘1’, the 24AAXXXE48
issues an acknowledge and transmits the 8-bit data
word. The master will not acknowledge the transfer, but
does generate a Stop condition, and the 24AAXXXE48
discontinues transmission (Figure 8-1).
8.2 Random Read
Random read operations allow the master to access
any memory location in a random manner. To perform
this type of read operation, the word address must first
be set. This is accomplished by sending the word
address to the 24AAXXXE48 as part of a write opera-
tion. Once the word address is sent, the master gener-
ates a Start condition following the acknowledge. This
terminates the write operation, but not before the inter-
nal Address Pointer is set. The master then issues the
control byte again, but with the R/W bit set to a ‘1’. The
24AAXXXE48 will then issue an acknowledge and
transmit the 8-bit data word. The master will not
acknowledge the transfer, but does generate a Stop
condition, and the 24AAXXXE48 will discontinue
transmission (Figure 8-2).
8.3 Sequential Read
Sequential reads are initiated in the same way as a
random read, except that once the 24AAXXXE48 trans-
mits the first data byte, the master issues an acknowl-
edge as opposed to a Stop condition in a random read.
This directs the 24AAXXXE48 to transmit the next
sequentially-addressed 8-bit word (Figure 8-3).
To provide sequential reads, the 24AAXXXE48 con-
tains an internal Address Pointer that is incremented by
one upon completion of each operation. This Address
Pointer allows the entire memory contents to be serially
read during one operation.
8.4 Noise Protection
The 24AAXXXE48 employs a VCC threshold detector
circuit which disables the internal erase/write logic if the
VCC is below 1.5V at nominal conditions.
The SCL and SDA inputs have Schmitt Trigger and
filter circuits which suppress noise spikes to assure
proper device operation, even on a noisy bus.
FIGURE 8-1:
CURRENT ADDRESS READ
S
Bus Activity
T
Control
Master
A
R
Byte
T
Data (n)
SDA Line
S 1 ^{0 1 0 A2* A1*A0* 1}
Bus Activity
A
Chip
Select
C
K
Bits
Note: * Bits A0, A1 and A2 are “don’t cares” for the 24AA02E48.
S
T
O
P
P
N
o
A
C
K
 2010 Microchip Technology Inc.
DS22124D-page 11