
X24320 
8 
Random Read  
Random  read  operation  allows  the  master  to  access any 
memory location in the array. Prior to issuing the 
Slave  Address  Byte  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   Byte   with   the   R/W   bit   low,   receives   an 
acknowledge,  then  issues  the Word  Address  Byte  1, 
receives another acknowledge, then issues the Word 
Address Byte 0. After the device acknowledges receipt of 
the Word Address Byte 0, the master issues another 
start condition and the Slave Address Byte with the  R/W bit 
set to one. This is followed by an acknowledge 
and then eight bits of data from the device. The master 
terminates the read operation by not responding with 
an  acknowledge  and  then  issuing  a  stop  condition. Refer  
to  figure  9  for  the  address,  acknowledge,  and 
data transfer sequence.  
The device will perform a similar operation called “Set Current  
Address”  if  a  stop  is  issued  instead  of  the 
second start shown in figure 9. The device will go into standby 
mode after the stop and all bus activity will be 
ignored until a start is detected. The effect of this operation   is   
that   the   new   address   is   loaded   into   the 
address counter, but no data is output by the device
.  
The  next  Current  Address  Read  operation  will  read from 
the newly loaded address.  
Sequential Read  
Sequential  reads  can  be  initiated  as  either  a  current 
address  read  or  random  read. The  first  Data  Byte  is 
transmitted  as  with  the  other  modes;  however,  the 
master now responds with an acknowledge, indicating 
it  requires  additional  data.  The  device  continues  to 
output   data   for   each   acknowledge   received.   The 
master terminates the read operation by not    responding  
with  an  acknowledge  and  then  issuing  a 
stop condition. 
The data output is sequential, with the data from address n 
followed by the data from address n + 1. The address 
counter for read operations increments through all byte 
addresses,  allowing  the  entire  memory  contents  to  be 
read  during  one  operation.  At  the  end  of  the  address 
space the counter “rolls over ” to address 0000h and the 
device  continues  to  output  data  for  each  acknowledge 
received.  Refer  to  figure  10  for  the  acknowledge  and 
data transfer sequence. 
SLAVE 
ADDRESS 
S 
S 
T 
O 
P 
A 
C 
K 
A 
C 
K 
A 
C 
K 
A 
C 
K 
DATA 
(1) 
DATA 
(2) 
SIGNALS 
FROM THE 
MASTER 
SDA BUS 
SIGNALS 
FROM THE 
SLAVE 
DATA 
(n–1) 
DATA 
(n) 
1 
(n is any integer greater than 1) 
P 
7035 FM 12 
SIGNALS 
FROM THE 
MASTER 
SDA BUS 
SIGNALS 
FROM THE 
SLAVE 
S 
T 
A 
R 
T 
SLAVE 
ADDRESS 
S 
T 
O 
P 
A 
C 
K 
A 
C 
K 
A 
C 
K 
WORD ADDRESS 
BYTE 1 
SLAVE 
ADDRESS 
0 
WORD ADDRESS 
BYTE 0 
S 
T 
A 
R 
T 
1 
DATA 
A 
C 
K 
S 
P 
S 
1  0  1  0 
7035 FM 11 
Figure 9. Random Read Sequence 
Figure 10. Sequential Read Sequence