NXP Semiconductors
NE1617A
Temperature monitor for microprocessor systems
8.6 SMBus interface
The device can communicate over a standard 2-wire serial interface System Management
Bus (SMBus) using the device pins SCLK and SDATA. The device employs four standard
SMBus protocols: write byte, read byte, send byte and receive byte. Data formats of those
protocols are shown in Figure 3 with following notifications:
• The SMBus master initiates data transfer by establishing a START condition (S) and
terminates data transfer by generating a STOP condition (P).
• Data is sent over the serial bus in sequence of 9 clock pulses according to each 8-bit
data byte followed by 1-bit status of the device acknowledgement.
• The 7-bit slave address is equivalent to the selected address of the device.
• The command byte is equivalent to the selected command of the device register.
• The ‘send byte’ format is often used for the one-shot conversion command.
• The ‘receive byte’ format is used for quicker transfer data from a device reading
register that was previously selected by a read byte format.
address
ACK
command
ACK
S 7 bits device address 0
8 bits device register
data
8 bits to register
ACK
P
START condition
R/W acknowledged
by device
acknowledged
by device
acknowledged STOP
by device condition
002aad523
a. Write byte format (for writing data byte to the device register)
address
ACK
command
ACK
address
ACK
S 7 bits device address 0
8 bits device register
S 7 bits device address 1
data
NACK
8 bits from register
P
START condition
R/W acknowledged
by device
acknowledged (re)START
by device condition
R/W acknowledged
by device
not STOP
acknowledged condition
by controller
002aad524
b. Read byte format (for reading data byte from the device register)
address
ACK
command
ACK
S 7 bits device address 0
8 bits device register
P
START condition
R/W acknowledged
by device
acknowledged STOP
by device condition
002aad525
c. Send byte format (for sending command without data, such as one-shot command)
address
ACK
S 7 bits device address 1
data
NACK
8 bits from register
P
START condition
R/W acknowledged
by device
not STOP
acknowledged condition
by controller 002aad526
d. Receive byte format (for continuously reading from device register)
Fig 3. SMBus programming format
NE1617A_4
Product data sheet
Rev. 04 — 30 July 2009
© NXP B.V. 2009. All rights reserved.
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