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參數(shù)資料
| 型號： | X1242 |
| 英文描述： | Real Time Clock/Calendar/Alarms/CPU Supervisor(實時時鐘/日歷/鬧鐘/帶EEPROM的監(jiān)控) |
| 中文描述： | 實時時鐘/日歷/報警/ CPU監(jiān)控（實時時鐘/日歷/鬧鐘/帶EEPROM中的監(jiān)控） |
| 文件頁數(shù)： | 13/24頁 |
| 文件大?。?/td> | 119K |
| 代理商： | X1242 |
X1242 – Preliminary Information
Characteristics subject to change without notice.
13 of 24
REV 1.1.3 10/15/00
www.xicor.com
Figure 17. Acknowledge Polling 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.
Random Read
Random read operations allows the master to access
any location in the X1242. 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 receipt
of each word address byte, the master immediately
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
data word. The master terminates the read operation
by not responding with an acknowledge and then issu-
ing a stop condition. Refer to Figure 18 for the
address, acknowledge, and data transfer sequence.
In a similar operation called “Set Current Address,” the
device sets the address if a stop is issued instead of
the second start shown in Figure 18. The X1242 then
goes into standby mode after the stop and all bus
activity will be ignored until a start is detected. This
operation loads the new address into the address
counter. The next Current Address Read operation will
read from the newly loaded address. This operation
could be useful if the master knows the next address it
needs to read, but is not ready for the data.
Sequential Read
Sequential reads can be initiated as either a current
address read or random address read. The first data
byte is transmitted as with the other modes; however,
the master now responds with an acknowledge, indi-
cating it requires additional data. The device continues
to output data for each acknowledge received. The
master terminates the read operation by not responding
with an acknowledge and then issuing a stop condition.
ACK
Returned
Issue Slave
Address Byte
(Read or Write)
Byte Load Completed
by Issuing STOP.
Enter ACK Polling
Issue STOP
Issue START
NO
YES
Issue STOP
NO
Continue Normal
Read or Write
Command
Sequence
PROCEED
YES
Nonvolatile Write
Cycle Complete.
Continue Command
Sequence
Figure 18.
Random Address Read Sequence
0
Slave
Address
Word
Address 1
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
A
C
K
Word
Address 0
1
1
1
1
0 0 0 0 0
1
1
1
1
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