![](http://datasheet.mmic.net.cn/300000/S42WD61S2-7P_datasheet_16209028/S42WD61S2-7P_12.png)
12
S4242/S42WD42/S4261/S42WD61
2025 6.0 4/17/00
FIGURE 14. SEQUENTIAL READ OPERATION (starting with a Random Address READ)
Sequential READ
Sequential READs can be initiated as either a current
address READ or random access READ. The first word is
transmitted as with the other byte read modes (current
address byte READ or random address byte READ);
however, the master now responds with an ACKnowledge,
indicating that it requires additional data from the
S42xxx. The S42xxx continues to output data for each
ACKnowledge received. The master terminates the se-
quential READ operation by not responding with an
ACKnowledge, and issues a STOP conditions.
During a sequential read operation, the internal address
counter is automatically incremented with each acknowl-
edge signal. For read operations, all address bits are
incremented, allowing the entire array to be read using a
single read command. After a count of the last memory
address, the address counter will
‘
roll-over
’
and the
memory will continue to output data. See Figure 14 for the
address, acknowledge and data transfer sequence.
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
D
7
D
6
D
5
D
4
D
3
D
2
D
1
D
0
A
7
A
6
A
5
A
4
A
3
A
2
A
1
A
0
Shading Denotes
42xxx
SDA Output Active
* S4261/S42WD61 only
S
T
A
R
T
Word Address
S
T
O
P
A
C
K
Acknowledges from 42xxx
Slave Address
Slave Address
Device
Type
Address
Read/Write
0= Write
Device
Type
Address
A10,A9,A8
A10,A9,A80
SDA Bus
Activity
S
T
A
R
T
Read/Write
1= Read
A
9
R
W
A
10
Acknowledge from
Master Receiver
A
C
K
A
C
K
A
C
K
Master sends Read
request to Slave
Master Writes Word
Address to Slave
Master Requests
Data from Slave
Slave sends
Data to Master
Slave Transmitter
to
Master Receiver
Slave Transmitter
to
Master Receiver
Master Transmitter
to
Slave Receiver
1 0 1 0
1 0 1 0
1
0
Slave sends
Data to Master
*
A
10
*
A
9
R
W
*
A
8
A
8
Lack of ACK (low)
determines last
data byte to be read
1
Lack of
Acknowledge from
Master Receiver
Slave Transmitter
to
Master Receiver
Master Transmitter
to
Slave Receiver
Master Transmitter
to
Slave Receiver
Master Transmitter
to
Slave Receiver
Slave Transmitter
to
Master Receiver
Slave Transmitter
to
Master Receiver
Last Data Byte
First Data Byte
2025 ILL14.1