LX1977IDU MICROSEMI [Microsemi Corporation], LX1977IDU Datasheet - Page 6

• Manufacturer Part Number: LX1977IDU
• Description: SMBus Ambient Light Sensor
• Manufacturer: MICROSEMI [Microsemi Corporation]

Copyright © 2010
Rev. 1.0, 2010-03-25
of data sent from the host will be a Data Byte or a Command
Code (also called index), depending on whether there is a Stop
Condition afterwards. If there is a Stop Condition, then the
received byte is a data byte (not a Command Code or register
index) to the LX1977 and this command will be sent to register
00h and executed. Note that this is considered a Send Byte
Protocol, which can only be used on register 00h as stated before.
If there is no Stop Condition detected, then the received byte is a
Command Code (or register index). In this case, either one or two
bytes of data will follow. The index points to an internal register
in the LX1977 that will be the object of the subsequent data
transfer.
of a valid index. After the index, there will be another byte /
word of data; this byte of data will be loaded into the indexed
register. In LX1977 Read / Write word protocols, the Command
Code (or register index) will always be the lower byte data
register address. The higher byte of the data will be loaded into
the register corresponding to the lower byte register index /
command code incremented by 1.
the device status bits by issuing a simple Receive Byte protocol.
In this command line, the W/R bit is set to a “1”. Upon the
receipt of a Receive Byte protocol, the LX1977 will
acknowledge that it has detected its address and a valid W/R bit;
the device will then put a copy of the register 00h data onto the
bus.
acknowledged the receipt of the data byte(s) followed by a
“Stop Condition”, and until the next “Start Condition” is
detected. Note that receipt of a “Stop Condition” or “Start
Condition” will reset the address detection state machine. The
LX1977 does not support “Packet Error Code”.
within the LX1977 using a Read Byte / Word protocol. In this
protocol, the host first will send a Write command indicating the
device address and Command Code. After the write command is
issued, the host initiates a repeat “Start Condition” followed by
issuing a Read from device’s address.
W/R bit is a “0”, signifying a “Write” command, the next byte
In a Write protocol, the LX1977 will acknowledge the receipt
The host can read the contents of register 00h which contains
The LX1977 will ignore all additional bus activity once it has
The host can read the contents of the indexed register(s)
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register(s) to be read. The repeat “Start Condition” will be
followed by the Slave address (refer to Table 11 and Table 12)
and a read command bit. Upon receipt of a Read command, the
LX1977 will acknowledge that it has detected its address and a
valid Read bit. Subsequently, one byte of data starting from the
indexed register address will be put onto the bus. A NACK from
the host signifies the end of the Read command. If instead, an
ACK is received, then the LX1977 will put another byte of data
from the next incremented register address onto the bus. A
NACK will signify the end of the Read command. Once the
LX1977 has placed the byte(s) of data on the serial bus, it will
ignore all additional bus activity until the next “Start Condition”
is detected.
In Read protocol, the Command Code is the index of the
SMBus Ambient Light Sensor
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ATASHEET
LX1977
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