ISL6425 Datasheet, PDF (9/12 Pages) Intersil Corporation – Single Output LNB Supply and Control Voltage Regulator with I2C Interface for Advanced Satellite Set-top Box Designs

ISL6425
SDA
SCL
S
P
START
CONDITION
STOP
CONDITION
FIGURE 2. START AND STOP WAVEFORMS
Byte Format
Every byte put on the SDA line must be 8 bits long. The number
of bytes that can be transmitted per transfer is unrestricted.
Each byte has to be followed by an acknowledge bit. Data is
transferred with the most significant bit first (MSB).
Acknowledge
The master (microprocessor) puts a resistive HIGH level on
the SDA line during the acknowledge clock pulse (Figure 3).
The peripheral that acknowledges has to pull down (LOW)
the SDA line during the acknowledge clock pulse, so that the
SDA line is stable LOW during this clock pulse. (Of course,
set-up and hold times must also be taken into account.)
The peripheral which has been addressed has to generate
an acknowledge after the reception of each byte, otherwise
the SDA line remains at the HIGH level during the ninth
clock pulse time. In this case, the master transmitter can
generate the STOP information in order to abort the transfer.
The ISL6425 will not generate the acknowledge if the
POWER OK signal from the UVLO is LOW.
SCL
1
2
8
9
SDA
START
MSB
ACKNOWLEDGE
FROM SLAVE
FIGURE 3. ACKNOWLEDGE ON THE I²C BUS
Transmission Without Acknowledge
Avoiding detection of the acknowledgement, the
microprocessor can use a simpler transmission; it waits one
clock without checking the slave acknowledging, and sends
the new data.
This approach, though, is less protected from error and
decreases the noise immunity.
ISL6425 Software Description
Interface Protocol
The interface protocol is comprised of the following, as
shown below in Table 2:
• A start condition (S)
• A chip address byte (MSB on left; the LSB bit determines
read (1) or write (0) transmission) (the assigned I²C slave
address for the ISL6425 is 0001 00XX)
• A sequence of data (1 byte + Acknowledge)
• A stop condition (P)
TABLE 2. INTERFACE PROTOCOL
S 0 0 0 1 0 0 0 R/W ACK Data (8 bits) ACK P
Transmitted Data (I²C bus WRITE mode)
When the R/W bit in the chip is set to 0, the main
microprocessor can write on the system register (SR1) of the
ISL6425 via I²C bus. These will be written by the
microprocessor as shown below.
R, W
SR1
R, W
DCL
R, W
R, W
SR2
X
System Register Format
• R, W = Read and Write bit
• R = Read-only bit
All bits reset to 0 at Power-On
TABLE 3. SYSTEM REGISTER 1 (SR1)
R, W
R, W
R, W
X
ENT1
LLC1
TABLE 4. SYSTEM REGISTER 2 (SR2)
R, W
R, W
R, W
X
X
X
R, W
VSEL1
R, W
EN2
R, W
EN1
R
OTF
R
OLF1
R
X
9
FN9176.1
February 8, 2005