© 2009 Microchip Technology Inc. DS22184A-page 11
24AA32AF/24LC32AF
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
control byte 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 24XX32AF contains an address counter that main-
tains the address of the last word accessed, internally
incremented by ‘1’. Therefore, if the previous read
access was to address ‘n’ (n is any legal address), the
next current address read operation would access data
from address n + 1.
Upon receipt of the control byte with R/W
bit set to ‘1’,
the 24XX32AF 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
24XX32AF 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 24XX32AF as part of a write operation
(R/W
bit set to ‘0’). Once the word address is sent, the
master generates a Start condition following the
acknowledge. This terminates the write operation, but
not before the internal Address Pointer is set. The
master issues the control byte again, but with the R/W
bit set to a ‘1’. The 24XX32AF 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 which causes the
24XX32AF to discontinue transmission (Figure 8-2).
After a random Read command, the internal address
counter will point to the address location following the
one that was just read.
8.3 Sequential Read
Sequential reads are initiated in the same way as a
random read, except that once the 24XX32AF trans-
mits the first data byte, the master issues an acknowl-
edge as opposed to the Stop condition used in a
random read. This acknowledge directs the 24XX32AF
to transmit the next sequentially addressed 8-bit word
(Figure 8-3). Following the final byte transmitted to the
master, the master will NOT generate an acknowledge,
but will generate a Stop condition. To provide sequen-
tial reads, the 24XX32AF contains an internal Address
Pointer which is incremented by ‘1’ upon completion of
each operation. This Address Pointer allows the entire
memory contents to be serially read during one
operation. The internal Address Pointer will automati-
cally roll over from address FFF to address 000 if the
master acknowledges the byte received from the array
address FFF.
FIGURE 8-1: CURRENT ADDRESS READ
SP
Bus Activity
Master
SDA Line
Bus Activity
S
T
O
P
Control
Byte
Data (n)
A
C
K
N
O
A
C
K
S
T
A
R
T
