© 2008 Microchip Technology Inc. DS22116A-page 11
24VL014H
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 ‘1’. There are three basic types
of read operations: current address read, random read
and sequential read.
8.1 Current Address Read
The 24VL014H 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 ‘1’,
the 24VL014H 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
24VL014H 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 done by sending the word address to the
24VL014H as part of a write operation.
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 then issues
the control byte again but with the R/W
bit set to a ‘1’.
The 24VL014H will then issue an acknowledge and
transmits the eight-bit data word. The master will not
acknowledge the transfer, but does generate a Stop
condition and the 24VL014H 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 24VL014H transmits
the first data byte, the master issues an acknowledge
as opposed to a Stop condition in a random read. This
directs the 24VL014H to transmit the next sequentially
addressed 8-bit word (Figure 8-3).
To provide sequential reads, the 24VL014H contains
an internal Address Pointer which is incremented by
one at the completion of each operation. This Address
Pointer allows the entire memory contents to be serially
read during one operation. The internal Address
Pointer will automatically roll over from address 7Fh to
address 00h.
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
