X24026
Current Address Read
Random Read
Internally the X24026 contains an address counter that
maintains the address of the last word accessed, incre-
mented by one. Therefore, if the last access (either a
read or write) was to address n, the next read operation
would access data from address n + 1. Upon receipt of
the slave address with the R/W bit set to one, the X24026
issues an acknowledge and transmits the eight bit word
during the next eight clock cycles. The master terminates
this transmission by issuing a stop condition, omitting the
ninth clock cycle acknowledge. Refer to Figure 7 for the
sequence of address, acknowledge and data transfer.
Random read operations allow the master to access any
memory location in a random manner. Prior to issuing
the slave address with the R/W bit set to one, the master
must first perform a “dummy” write operation.The master
issues the start condition, and the slave address followed
by the word address it is to read. After the word address
acknowledge, the master immediately reissues the start
condition and the slave address with the R/W bit set to
one. This will be followed by an acknowledge from the
X24026 and then by the eight bit word.The master termi-
nates this transmission by issuing a stop condition, omit-
ting the ninth clock cycle acknowledge. Refer to Figure 8
for the address, acknowledge and data transfer
sequence.
Figure 7. Current Address Read
S
T
A
R
T
S
SLAVE
ADDRESS
BUS ACTIVITY:
MASTER
T
DATA
O
P
SDA LINE
S
P
A
C
K
BUS ACTIVITY:
X24026
7020 FRM 10
Figure 8. Random Read
S
T
A
R
T
S
T
A
R
T
S
T
O
P
SLAVE
ADDRESS
WORD
ADDRESS n
SLAVE
ADDRESS
BUS ACTIVITY:
MASTER
DATA n
SDA LINE
S
S
P
A
C
K
A
C
K
A
C
K
BUS ACTIVITY:
X24026
7020 FRM 11
7
XICOR [ XICOR INC. ]
