X1243 Datasheet, PDF (10/18 Pages) Xicor Inc. – Real Time Clock/Calendar/Alarm with EEPROM

X1243
the address counter would point to location 7 on the
page that was just written. If the master supplies more
than the maximum bytes in a page, then the previously
loaded data is over written by the new data, one byte
at a time.
The master terminates the Data Byte loading by issu-
ing a stop condition, which causes the device to begin
the non-volatile write cycle. As with the byte write
operation, all inputs are disabled until completion of
the internal write cycle. Refer to Figure 8 for the
address, acknowledge, and data transfer 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 and it’s associated ACK signal. If a stop is issued
in the middle of a data byte, or before 1 full data byte +
ACK is sent, then the device will reset itself without
performing the write. The contents of the array will not
be affected.
Acknowledge Polling
The disabling of the inputs during non-volatile write
cycles can be used to take advantage of the typical
5mS write cycle time. Once the stop condition is
issued to indicate the end of the master’s byte load
operation, the device initiates the internal non-volatile
write cycle. Acknowledge polling can be initiated
immediately. To do this, the master issues a start con-
dition followed by the Slave Address Byte for a write or
read operation. If the device is still busy with the non-
volatile write 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. Refer to the flow chart in Table 9.
READ OPERATIONS
There are three basic read operations: Current
Address Read, Random Read, and Sequential Read.
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 sixteen bit
address is initialized to 0h. In this way, a current
address read can be initiated immediately after the
power on reset to download the contents of memory
starting at the first location.
Byte load completed
by issuing STOP.
Enter ACK Polling
Issue START
Issue Slave
Address Byte
(Read or Write)
ACK
returned?
YES
nonvolatile write
Cycle complete.
Continue command
sequence?
YES
Continue normal
Read or Write
command
sequence
Issue STOP
NO
NO
Issue STOP
PROCEED
Figure 9. Acknowledge Polling Sequence
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 10
for the address, acknowledge, and data transfer
sequence.
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 condi-
tion during the ninth cycle or hold SDA HIGH during
the ninth clock cycle and then issue a stop condition.
10