|X1226V8||4K (512 x 8), 2-Wire™ RTC|
|X1226V8 Datasheet PDF : 25 Pages |
Figure 4. Valid Start and Stop Conditions
Figure 5. Acknowledge Response From Receiver
Following a start condition, the master must output a
Slave Address Byte. The first four bits of the Slave
Address Byte specify access to either the EEPROM
array or to the CCR. Slave bits ‘1010’ access the
EEPROM array. Slave bits ‘1101’ access the CCR.
When shipped from the factory, EEPROM array is
UNDEFINED, and should be programmed by the cus-
tomer to a known state.
Bit 3 through Bit 1 of the slave byte specify the device
select bits. These are set to ‘111’.
The last bit of the Slave Address Byte defines the
operation to be performed. When this R/W bit is a one,
then a read operation is selected. A zero selects a
write operation. Refer to Figure 6.
After loading the entire Slave Address Byte from the
SDA bus, the X1226 compares the device identifier
and device select bits with ‘1010111’ or ‘1101111’.
Upon a correct compare, the device outputs an
acknowledge on the SDA line.
Following the Slave Byte is a two byte word address.
The word address is either supplied by the master
device or obtained from an internal counter. On power-
up the internal address counter is set to address 0h,
so a current address read of the EEPROM array starts
at address 0. When required, as part of a random
read, the master must supply the 2 Word Address
Bytes as shown in Figure 6.
In a random read operation, the slave byte in the
“dummy write” portion must match the slave byte in
the “read” section. That is if the random read is from
the array the slave byte must be 1010111x in both
instances. Similarly, for a random read of the
Clock/Control Registers, the slave byte must be
1101111x in both places.
May 8, 2006
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