X1240
DEVICE ADDRESSING
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 device must supply the 2 Word
Address Bytes.
Following a start condition, the master must output a
Slave Address Byte. The first four bits of the Slave
Address Byte specify access to the EEPROM array or
to the CCR. Slave bits ‘1010’ access the EEPROM
array. Slave bits ‘1101’ access the CCR.
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
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 12.
After loading the entire Slave Address Byte from the
SDA bus, the device 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.
Figure 12. Sequential Read Sequence
S
Slave
Address
A
C
K
A
C
K
A
C
K
Signals from
the Master
t
o
p
SDA Bus
1
A
C
K
Signals from
the Slave
Data
(2)
Data
(n-1)
Data
(1)
Data
(n)
(n is any integer greater than 1)
11
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