24AA32A/24LC32A
DS21713G-page 10 © 2006 Microchip Technology Inc.
6.0 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.
6.1 Current Address Read
The 24XX32A 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 24XX32A 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
24XX32A discontinues transmission (Figure 6-1).
6.2 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 24XX32A 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 24XX32A 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 24XX32A
to discontinue transmission (Figure 6-2). After a
random Read command, the internal address counter
will point to the address location following the one that
was just read.
6.3 Sequential Read
Sequential reads are initiated in the same way as a
random read, except that once the 24XX32A transmits
the first data byte, the master issues an acknowledge
as opposed to the Stop condition used in a random
read. This acknowledge directs the 24XX32A to
transmit the next sequentially addressed 8-bit word
(Figure 6-3). 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 24XX32A 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 6-1: 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
