ISL12021 Datasheet, PDF (19/24 Pages) Intersil Corporation – Real Time Clock with On Chip Temp Compensation ±5ppm

ISL12021
TEMP Registers (TEMP)
The temperature sensor produces an analog voltage output
and is input to an A/D converter which outputs a 10-bit
temperature value in degrees Kelvin. The output is coded to
produce greater resolution for the temperature control.
TK07:00 are the LSBs of the code, and TK09:08 are the
MSBs of the code. The output code can be converted to
degrees Centigrade by first converting from binary to
decimal and then subtracting 369d.
Temperature in °C = [(TK <9:0>)/2] - 369
(EQ. 1)
The practical range for the temp sensor register output is
from 658d to 908d, or -40°C to +85°C.
The TSE bit must be set to “1” to enable temperature
sensing.
TABLE 22.
TK0L
TK0M
7
6
5
4
3
2
1
0
TK07 TK06 TK05 TK04 TK03 TK02 TK01 TK00
0 0 0 0 0 0 TK09 TK08
User Registers (accessed by using Slave
Address 1010111x)
Addresses [00h to 7Fh]
These registers are 128 bytes of battery-backed user SRAM.
I²C Serial Interface
The ISL12021 supports a bi-directional bus oriented
protocol. The protocol defines any device that sends data
onto the bus as a transmitter and the receiving device as the
receiver. The device controlling the transfer is the master
and the device being controlled is the slave. The master
always initiates data transfers and provides the clock for
both transmit and receive operations. Therefore, the
ISL12021 operates as a slave device in all applications.
All communication over the I²C interface is conducted by
sending the MSB of each byte of data first.
Protocol Conventions
Data states on the SDA line can change only during SCL
LOW periods. SDA state changes during SCL HIGH are
reserved for indicating START and STOP conditions (See
Figure 7). On power up of the ISL12021, the SDA pin is in
the input mode.
All I²C interface operations must begin with a START
condition, which is a HIGH to LOW transition of SDA while
SCL is HIGH. The ISL12021 continuously monitors the SDA
and SCL lines for the START condition and does not
respond to any command until this condition is met (See
Figure 7). A START condition is ignored during the power-up
sequence.
All I²C interface operations must be terminated by a STOP
condition, which is a LOW to HIGH transition of SDA while
SCL is HIGH (See Figure 7). A STOP condition at the end of
a read operation or at the end of a write operation to memory
only places the device in its standby mode.
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 8).
The ISL12021 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
ISL12021 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.
SCL
SDA
START
DATA
DATA
DATA
STABLE CHANGE STABLE
STOP
FIGURE 7. VALID DATA CHANGES, START AND STOP CONDITIONS
19
FN6451.0
March 30, 2007