X1205 Xicor, X1205 Datasheet - Page 11

• Manufacturer Part Number: X1205
• Description: Real Time Clock/Calendar
• Manufacturer: Xicor

X1205 – Preliminary Information
Random Read
Random read operations allow the master to access
any location in the X1205. Prior to issuing the Slave
Address Byte with the R/W bit set to zero, 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 10 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 10. The X1205 then
goes into standby mode after the stop and all bus
Figure 10. Random Address Read Sequence
Figure 11. Sequential Read Sequence
REV 1.0.9 8/29/02
Signals from
the Master
SDA Bus
Signals from
the Slave
Signals from
the Master
SDA Bus
Signals from
the Slave
S
a
r
t
t
1
Address
1
Slave
Address
0
Slave
1
1
1
A
C
K
1
1
0
A
C
K
Data
0 0 0 0 0 0 0
(1)
Address 1
Word
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A
C
K
C
A
K
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 mas-
ter terminates the read operation by not responding with
an acknowledge and then issuing a stop condition.
The data output is sequential, with the data from
address n followed by the data from address n + 1.
Refer to Figure 11 for the acknowledge and data trans-
fer sequence.
Address 0
Data
(2)
Word
C
A
K
A
C
K
(n is any integer greater than 1)
S
a
t
r
t
1
1
Address
Data
(n-1)
Characteristics subject to change without notice.
Slave
0
1
1
1
1
1
A
C
K
A
C
K
Data
Data
(n)
S
o
p
t
S
o
p
t
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