X1227
Figure 7. Valid Data Changes on the SDA Bus
SCL
SDA
Data Stable
Data Change
Data Stable
Figure 8. Valid Start and Stop Conditions
SCL
SDA
Start
Stop
Figure 9. Acknowledge Response From Receiver
SCL from
Master
1
8
9
Data Output
from Transmitter
Data Output
from Receiver
Start
Acknowledge
DEVICE ADDRESSING
and device select bits with ‘1010111’ or ‘1101111’.
Upon a correct compare, the device outputs an
acknowledge on the SDA line.
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.
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 10.
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’.
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.
The last bit of the Slave Address Byte defines the oper-
ation 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 10.
After loading the entire Slave Address Byte from the
SDA bus, the X1227 compares the device identifier
Characteristics subject to change without notice. 11 of 28
REV 1.1.20 1/13/03
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