ISL12008 Datasheet, PDF (15/19 Pages) Intersil Corporation – I2C Real Time Clock with Battery Backup

ISL12008
Device Addressing
Following a start condition, the master must output a Slave
Address Byte. The 7 MSBs are the device identifiers. These
bits are “1101000”.
The last bit of the Slave Address Byte defines a read or write
operation to be performed. When this R/W bit is a “1”, then a
read operation is selected (refer to Figure 16). When this
R/W bit is a “0” , then a write operation (refer to Figure 12).
After loading the entire Slave Address Byte from the SDA
bus, the ISL12008 compares the Slave bit and device select
bits with “1101000”. Upon a correct compare, the device
outputs an acknowledge on the SDA line.
Following the Slave Byte is a one 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 CCR array starts at address 0h. When required,
as part of a random read, the master must supply the 1 Word
Address Bytes, as shown in Figure 14.
In a random read operation, the slave byte in the “dummy
write” portion must match the slave byte in the “read”
section. For a random read of the Clock/Control Registers,
the slave byte must be “1101000x” in both places.
1
1
0
1
00
0
R/W
SLAVE
ADDRESS BYTE
A7 A6 A5 A4 A3 A2 A1 A0 WORD ADDRESS
Write Operation
A Write operation requires a START condition, followed by a
valid Identification Byte, a valid Address Byte, a Data Byte,
and a STOP condition. After each of the three bytes, the
ISL12008 responds with an ACK. After received the STOP
condition, the ISL12008 writes the data into the memory,
then the I²C bus enters a standby state. After a Write
operation, the internal address pointer will remain at the
address for the last data byte written.
Read Operation
A Read operation consists of a three byte instruction
followed by one or more Data Bytes (see Figure 14). The
master initiates the operation issuing the following
sequence: a START, the Identification byte with the R/W bit
set to “0”, an Address Byte, a second START, and a second
Identification byte with the R/W bit set to “1”. After each of
the three bytes, the ISL12008 responds with an ACK. Then
the ISL12008 transmits Data Bytes as long as the master
responds with an ACK during the SCL cycle following the
eighth bit of each byte. The master terminates the read
operation (issuing a STOP condition) following the last bit of
the last Data Byte (see Figure 14).
The Data Bytes are from the memory location indicated by
an internal address pointer. This internal address pointer
initial value is determined by the Address Byte in the Read
operation instruction, and increments by one during
transmission of each Data Byte.
D7 D6 D5 D4 D3 D2 D1 D0 DATA BYTE
FIGURE 13. SLAVE ADDRESS, WORD ADDRESS, AND DATA
BYTES
SIGNALS
FROM THE
MASTER
S
T _{IDENTIFICATION}
A
BYTE WITH
R
T
R/W = 0
ADDRESS
BYTE
S
T _{IDENTIFICATION}
A
R
T
BYTE WITH
R/W = 1
S
A
A
T
C
C
O
K
K
P
SIGNAL AT
SDA
11010000
A
SIGNALS FROM
C
THE SLAVE
K
11010001
A
A
C
C _{FIRST READ}
K
K _{DATA BYTE}
LAST READ
DATA BYTE
FIGURE 14. READ SEQUENCE
15
FN6690.1
September 26, 2008