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