X24320
Acknowledge Polling
The maximum write cycle time can be significantly
reduced using Acknowledge Polling. To initiate
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,
Random Reads, and Sequential Reads.
Current Address Read
Internally, the device contains an address counter that
maintains the address of the last word read or written
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
the last address in a given page, the counter will “roll
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
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.
Acknowledge Polling, 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
internal write cycle, then no ACK will be returned. If the
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 .
Figure 7. Acknowledge Polling Sequence
BYTE LOAD COMPLETED
BY ISSUING STOP.
ENTER ACK POLLING
ISSUE
START
ISSUE SLAVE
ADDRESS BYTE
ISSUE STOP
(READ OR WRITE)
ACK
RETURNED?
NO
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.
YES
HIGH
VOLTAGE
CYCLE COMPLETE.
CONTINUE
NO
Figure 8. Current Address Read Sequence
SIGNALS
FROM THE
MASTER
S
T
SEQUENCE?
YES
SDA BUS
CONTINUE NORMAL
READ OR WRITE
A
R
SLAVE
ADDRESS
S
T
O
P
T
S 1 01 0
1
A
C
P
DATA
7035 FM 10
ISSUE STOP
COMMAND SEQUENCE
SIGNALS
FROM THE
SLAVE
K
PROCEED
7035 FM 09
7
ICMIC [ IC MICROSYSTEMS ]
