24AA00/24LC00/24C00
DS21178D-page 8
2003 Microchip Technology Inc.
8.0
READ OPERATIONS
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 one. There are three basic types
of read operations: current address read, random read,
and sequential read.
8.1
Current Address Read
The 24XX00 contains an address counter that main-
tains the address of the last word accessed, internally
incremented by one. Therefore, if the previous read
access was to address n, the next current address read
operation would access data from address n + 1. Upon
receipt of the slave address with the R/W bit set to one,
the device issues an acknowledge and transmits the
eight-bit data word. The master will not acknowledge
the transfer but does generate a Stop condition and the
device 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, first the word address must
be set. This is done by sending the word address to the
device as part of a write operation.
After the word address is sent, the master generates a
Start condition following the acknowledge. This termi-
nates the write operation, but not before the internal
address pointer is set. Then the master issues the
control byte again but with the R/W bit set to a one. The
24XX00 will then issue an acknowledge and transmits
the eight bit data word. The master will not acknowl-
edge the transfer but does generate a Stop condition
and the device discontinues transmission (Figure 8-2).
After this 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 after the device transmits the
first data byte, the master issues an acknowledge as
opposed to a Stop condition in a random read. This
directs the device to transmit the next sequentially
addressed 8-bit word (Figure 8-3).
To provide sequential reads the 24XX00 contains an
internal address pointer which is incremented by one at
the completion of each read operation. This address
pointer allows the entire memory contents to be serially
read during one operation.
FIGURE 8-1:
CURRENT ADDRESS READ
BUS ACTIVITY
MASTER
SDA LINE
BUS ACTIVITY
P
S
S
T
O
P
CONTROL
BYTE
S
T
A
R
T
DATA
A
C
K
N
O
A
C
K
1
1
0
0 X X X 1
X = Don’t Care Bit