ISL12022MA_10 Datasheet, PDF (25/29 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation and Auto Daylight Saving

ISL12022MA
SCL
SDA
START
DATA
DATA DATA
STABLE CHANGE STABLE
STOP
FIGURE 15. VALID DATA CHANGES, START AND STOP CONDITIONS
SCL FROM
MASTER
1
SDA OUTPUT FROM
TRANSMITTER
8
9
HIGH IMPEDANCE
SDA OUTPUT
FROM RECEIVER
HIGH
START
ACK
FIGURE 16. ACKNOWLEDGE RESPONSE FROM RECEIVER
SIGNALS FROM
THE MASTER
WRITE
S
T
A ^{IDENTIFICATION}
R
BYTE
T
ADDRESS
BYTE
S
DATA
T
BYTE
O
P
SIGNAL AT SDA
11011110 0000
SIGNALS FROM
THE
A
A
A
C
C
C
K
K
K
FIGURE 17. BYTE WRITE SEQUENCE (SLAVE ADDRESS FOR CSR SHOWN)
An acknowledge (ACK) is a software convention used to
indicate a successful data transfer. The transmitting
device, either master or slave, releases the SDA bus
after transmitting eight bits. During the ninth clock cycle,
the receiver pulls the SDA line LOW to acknowledge the
reception of the eight bits of data (see Figure 16).
The ISL12022MA responds with an ACK after recognition
of a START condition followed by a valid Identification
Byte, and once again, after successful receipt of an
Address Byte. The ISL12022MA also responds with an
ACK after receiving a Data Byte of a write operation. The
master must respond with an ACK after receiving a Data
Byte of a read operation.
Device Addressing
Following a start condition, the master must output a
Slave Address Byte. The 7 MSBs are the device
identifiers. These bits are “1101111” for the RTC
registers and “1010111” for the User SRAM.
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”, a read operation is selected. A “0” selects a write
operation (refer to Figure 18).
After loading the entire Slave Address Byte from the SDA
bus, the ISL12022MA compares the device identifier and
device select bits with “1101111” or “1010111”. Upon a
correct compare, the device outputs an acknowledge on
the SDA line.
1
1
0
1
11
1
R/
SLAVE
ADDRESS BYTE
A7 A6 A5 A4 A3 A2 A1 A0 WORD
ADDRESS
D7 D6 D5 D4 D3 D2 D1 D0 DATA BYTE
FIGURE 18. SLAVE ADDRESS, WORD ADDRESS, AND
DATA BYTES
25
FN7575.1
July 9, 2010