S4242/S42WD42/S4261/S42WD61
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.
Acknowledges from 42xxx
Acknowledge from
Master Receiver
Lack of
Acknowledge from
Master Receiver
SDA Bus
Activity
1 0 1 0
S
T Device
A Type
R Address
T
* * *
A A A R
10 9 8 W
A
C
Word Address
K
A A A A A A A A
7 6 5 4 3 2 1 0
A
C
K
A A A R
10 9 8 W
A
C
K
A
First Data Byte
C
K
D D D D D D D D
7 6 5 4 3 2 1 0
Last Data Byte
0
1 0 1 0
1
D D D D D D D D
7 6 5 4 3 2 1 0
1
S
T
O
P
A10,A9,A8
Read/Write
0= Write
S
T Device
A
Type
A10,A9,A80
R Address
Read/Write
T
1= Read
Slave Address
Master sends Read
request to Slave
Master Writes Word
Address to Slave
Slave Address
Master Requests
Data from Slave
Slave sends
Data to Master
Lack of ACK (low)
determines last
data byte to be read
Slave sends
Data to Master
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
Slave Transmitter
to
Master Receiver
Slave Transmitter
to
Master Receiver
Slave Transmitter
to
Master Receiver
Master Transmitter
to
Slave Receiver
2025 ILL14.1
Shading Denotes
42xxx
SDA Output Active
* S4261/S42WD61 only
FIGURE 14. SEQUENTIAL READ OPERATION (starting with a Random Address READ)
2025 6.0 4/17/00
12
SUMMIT [ SUMMIT MICROELECTRONICS, INC. ]
