X24320
READ OPERATIONS
Read operations are initiated in the same manner as write
operations with the exception that the R/W bit of
Acknowledge Polling
The maximum write cycle time can be significantly
reduced using Acknowledge Polling. To initiate
the Slave Address Byte is set to one. There are three basic
read operations: Current Address Reads,
Acknowledge Polling, the master issues a start condition
followed by the Slave Address Byte for a write or
Random Reads, and Sequential Reads.
read operation. If the device is still busy with the
internal write cycle, then no ACK will be returned. If the
Current Address Read
Internally, the device contains an address counter that
maintains the address of the last word read or written
device has completed the internal write operation, an ACK
will be returned and the host can then proceed
with the read or write operation. Refer to figure 7 .
incremented by one. After a read operation from the last
address in the array, the counter will “roll over” to the first
address in the array. After a write operation to
Figure 7. Acknowledge Polling Sequence
the last address in a given page, the counter will “roll
BYTE LOAD COMPLETED
BY ISSUING STOP.
ENTER ACK POLLING
over” to the first address on the same page.
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
ISSUE
START
respond with an acknowledge during the ninth clock and
then issues a stop condition. Refer to figure 8 for the address
acknowledge, and data transfer sequence.
ISSUE SLAVE
ADDRESS BYTE
ISSUE STOP
(READ OR WRITE)
It should be noted that the ninth clock cycle of the read
operation is not a “don’t care "
.” To terminate a read
operation, the master must either issue a stop condition
during the ninth cycle or hold SDA HIGH during
the ninth clock cycle and then issue a stop condition.
ACK
RETURNED?
NO
YES
HIGH
VOLTAGE
Figure 8. Current Address Read Sequence
NO
CYCLE COMPLETE.
CONTINUE
SEQUENCE?
S
T
A
R
T
SIGNALS
FROM THE
MASTER
S
T
SLAVE
ADDRESS
O
P
YES
SDA BUS
S 1 01 0
1
P
CONTINUE NORMAL
READ OR WRITE
COMMAND SEQUENCE
A
C
K
ISSUE STOP
SIGNALS
FROM THE
SLAVE
DATA
7035 FM 10
PROCEED
7035 FM 09
7
ICMIC [ IC MICROSYSTEMS ]
