ISL12020MIRZ-T7A Datasheet, PDF (27/34 Pages) Intersil Corporation – Low Power RTC with Battery Backed SRAM, Integrated ±5ppm Temperature Compensation and Auto Daylight Saving

ISL12020M
SIGNALS FROM
THE MASTER
WRITE
S
T
A
R
IDENTIFICATION
BYTE
ADDRESS
BYTE
T
S
DATA
T
BYTE
O
P
SIGNAL AT SDA
11011110 0000
SIGNALS FROM
THE ISL12020M
A
A
A
C
C
C
K
K
K
FIGURE 18. BYTE WRITE SEQUENCE (SLAVE ADDRESS FOR CSR SHOWN)
All I²C interface operations must begin with a START condition,
which is a HIGH to LOW transition of SDA while SCL is HIGH. The
ISL12020M 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 16). 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 16). 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
17).
The ISL12020M 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
ISL12020M 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 19).
After loading the entire Slave Address Byte from the SDA bus, the
ISL12020M 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.
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 00h, so a current address read starts at address 00h. When
required, as part of a random read, the master must supply the 1
Word Address Bytes, as shown in Figure 20.
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 Control/Status Registers, the slave byte must be
“1101111x” in both places.
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 19. SLAVE ADDRESS, WORD ADDRESS, AND DATA BYTES
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 ISL12020M
responds with an ACK. At this time, the I²C interface enters a
standby state.
Read Operation
A Read operation consists of a three byte instruction, followed by
one or more Data Bytes (see Figure 20). 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 ISL12020M responds
with an ACK. Then the ISL12020M 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 20).
The Data Bytes are from the memory location indicated by an
internal pointer. This pointer’s initial value is determined by the
Address Byte in the Read operation instruction, and increments
by one during transmission of each Data Byte. After reaching the
memory location 2Fh, the pointer “rolls over” to 00h, and the
device continues to output data for each ACK received.
27
FN6667.5
December 13, 2011