TC74A0-33VAT MICROCHIP [Microchip Technology], TC74A0-33VAT Datasheet - Page 8

• Manufacturer Part Number: TC74A0-33VAT
• Description: Tiny Serial Digital Thermal Sensor
• Manufacturer: MICROCHIP [Microchip Technology]

TC74
FIGURE 3-1:
3.3
The TC74 continuously monitors the SDA and SCL
lines for a START condition (a HIGH to LOW transition
of SDA while SCL is HIGH) and will not respond until
this condition is met.
3.4
Immediately following the START Condition, the host
must transmit the address byte to the TC74. The states
of A1 and A0 determine the 7-bit SMBus address for
the TC74. The 7-bit address transmitted in the serial bit
stream must match for the TC74 to respond with an
Acknowledge (indicating the TC74 is on the bus and
ready to accept data). The 8-bit in the Address Byte is
a Read/Write Bit. This bit is a ‘1’ for a read operation or
‘0’ for a write operation. During the first phase of any
transfer this bit will be set = 0 to indicate that the
command byte is being written.
3.5
Acknowledge (ACK) provides a positive handshake
between the host and the TC74. The host releases
SDA after transmitting 8 bits. The host then generates
a ninth clock cycle to allow the TC74 to pull the SDA
line LOW. This action acknowledges that the TC74
successfully received the previous eight bits of data or
address.
DS21462B-page 8
START Condition (S)
Address Byte
Acknowledge (ACK)
Write Byte Format
Read Byte Format
Receive Byte Format
S Address
S = START Condition
P = STOP Condition
Shaded = Slave Transmission
S
Slave Address
S
Address
7 Bits
7 Bits
Slave Address
SMBUS PROTOCOLS
Address
7 Bits
WR
RD ACK
ACK
Command Byte: selects
which register you are
reading from.
Command
WR
Data Byte: reads data from
the register commanded by
the last Read Byte or Write
Byte transmission.
Data
8 Bits
8 Bits
Nack
ACK
ACK
Command Byte: selects
which register you are
writing to.
P
Command
S
8 Bits
Slave Address: repeated
due to change in data-
flow direction.
3.6
After a successful ACK of the address byte, the host
must transmit the data byte to be written or clock in the
data to be read. (See the appropriate timing diagrams).
ACK will be generated after a successful write of a data
byte into the TC74.
3.7
Communications must be terminated by a STOP
condition (a LOW to HIGH transition of SDA while SCL
is HIGH). The STOP Condition must be communicated
by the transmitter to the TC74. NOTE: Refer to Timing
Diagrams for serial bus timing.
Address
7 Bits
Data Byte
STOP Condition (P)
ACK
RD ACK
Data Byte: data goes
into the register set
by the command byte.
Data
8 Bits
Data Byte: reads from
the register set by the
command byte.
©
Data
8 Bits
2002 Microchip Technology Inc.
ACK
NACK P
P