10
FN8111.0
March 28, 2005
Read Operation
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, receives an acknowledge, then
issues the Word Address Bytes. After acknowledging
receipts of the Word Address Bytes, the master immedi-
ately issues another start condition and the Slave
Address Byte with the R/W
bit set to one. This is followed
by an acknowledge from the device and then by the eight
bit word. The master terminates the read operation by
not responding with an acknowledge and then issuing a
stop condition. See Figure 12 for the address, acknowl-
edge, and data transfer sequence.
Figure 9. Read Sequence
Stops and Write Modes
Stop conditions that terminate write operations must
be sent by the master after sending at least 1 full data
byte plus the subsequent ACK signal. If a stop is
issued in the middle of a data byte, or before 1 full
data byte plus its associated ACK is sent, then the
device will reset itself without performing the write. The
contents of the array will not be effected.
Acknowledge Polling
The disabling of the inputs during high voltage cycles
can be used to take advantage of the typical 5ms write
cycle time. Once the stop condition is issued to indi-
cate the end of the master’s byte load operation, the
device initiates the internal high voltage cycle.
Acknowledge polling can be initiated immediately. To
do this, the master issues a start condition followed by
the Slave Address Byte for a write or read operation. If
the device is still busy with the high voltage cycle then
no ACK will be returned. If the device has completed
the write operation, an ACK will be returned and the
host can then proceed with the read or write operation.
See Figure 12.
Serial Read Operations
Read operations are initiated in the same manner as
write operations with the exception that the R/W
bit of
the Slave Address Byte is set to one. There are three
basic read operations: Current Address Reads, Ran-
dom Reads, and Sequential Reads.
Current Address Read
Internally the device contains an address counter that
maintains the address of the last word read incre-
mented by one. Therefore, if the last read was to
address n, the next read operation would access data
from address n+1. On power up, the address of the
address counter is undefined, requiring a read or write
operation for initialization.
Upon receipt of the Slave Address Byte with the R/W
bit set to one, the device issues an acknowledge and
then transmits the eight bits of the Data Byte. The
master terminates the read operation when it does not
respond with an acknowledge during the ninth clock
and then issues a stop condition. See Figure 13 for the
address, acknowledge, and data transfer sequence.
0
Slave
Address
Byte
Address
A
C
K
A
C
K
S
t
a
r
t
S
t
o
p
Slave
Address
Data
A
C
K
1
S
t
a
r
t
SDA Bus
Signals from
the Slave
Signals from
the Master
101
0
01
11111111
X40010, X40011, X40014, X40015
