S4242 データシートの表示（PDF） - Summit Microelectronics
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S4242 Datasheet PDF : 16 Pages
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S4242/S42WD42/S4261/S42WD61
Random Address Byte Read
Random address read operations allow the master to
access any memory location in a random fashion. This
operation involves a two-step process. First, the master
issues a write command which includes the start condi-
tion and the slave address field (with the R/W bit set to
WRITE) followed by the address of the word it is to read.
This procedure sets the internal address counter of the
S42xxx to the desired address.
After the word address acknowledge is received by the
master, the master immediately reissues a start condition
followed by another slave address field with the R/W bit
set to READ. The S42xxx will respond with an acknowl-
edge and then transmit the 8-data bits stored at the
addressed location. At this point, the master does not
acknowledge the transmission but does generate the stop
condition. The S42xxx discontinues data transmission
and reverts to its standby power mode. See Figure 13 for
the address, acknowledge and data transfer sequence.
SDA Bus
Activity
**
A
A
A A A R C Word Address C
10 9 8 W K
K
A
A AA R C
10 9 8 W K
Data Byte
101 0
0
S
T
A
Device
Type
Address
R
T
A10,A9,A8
Read/Write
0= Write
Slave Address
AAA A AA AA
765 4 32 10
101 0
1
S
T Device
A
R
Type
Address
A10,A9,A8
Read/Write
T
1= Read
Slave Address
D
7
DD
65
DD
43
DD
21
D
0
1
S
T
O
Lack of ACK (low) P
from Master
determines last
data byte to be read
Master sends Read
request to Slave
Master Writes Word
Address to Slave
Master Requests
Data from Slave
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
Shading Denotes
42xxx
SDA Output Active
Slave Transmitter
to
Master Receiver
Slave Transmitter
to
Master Receiver
Slave Transmitter
to
Master Receiver
* S4261/S42WD61 only
2025 ILL13.1
FIGURE 13. RANDOM ADDRESS BYTE READ MODE
2025 6.0 4/17/00
11
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