TCN75A_1 Datasheet, PDF (11/40 Pages) Microchip Technology – 2-Wire Serial Temperature Sensor

4.0 SERIAL COMMUNICATION
4.1 2-Wire SMBus/Standard Mode
I²C™ Protocol-Compatible
Interface
The TCN75A serial clock input (SCL) and the
bidirectional serial data line (SDA) form a 2-wire
bidirectional SMBus/Standard mode I²C compatible
communication port (refer to the Digital Input/output
Pin Characteristics Table and Serial Interface
Timing Specifications (Note 1) Table).
The following bus protocol has been defined:
TABLE 4-1: TCN75A SERIAL BUS
PROTOCOL DESCRIPTIONS
Term
Description
Master
Slave
Transmitter
Receiver
Start
Stop
Read/Write
ACK
NAK
Busy
Not Busy
Data Valid
The device that controls the serial bus,
typically a microcontroller.
The device addressed by the master,
such as the TCN75A.
Device sending data to the bus.
Device receiving data from the bus.
A unique signal from master to initiate
serial interface with a slave.
A unique signal from the master to
terminate serial interface from a slave.
A read or write to the TCN75A
registers.
A receiver Acknowledges (ACK) the
reception of each byte by polling the
bus.
A receiver Not-Acknowledges (NAK) or
releases the bus to show End-of-Data
(EOD).
Communication is not possible
because the bus is in use.
The bus is in the Idle state, both SDA
and SCL remain high.
SDA must remain stable before SCL
becomes high in order for a data bit to
be considered valid. During normal
data transfers, SDA only changes state
while SCL is low.
TCN75A
4.1.1 DATA TRANSFER
Data transfers are initiated by a Start condition (Start),
followed by a 7-bit device address and a read/write bit.
An Acknowledge (ACK) from the slave confirms the
reception of each byte. Each access must be
terminated by a Stop condition (Stop).
Repeated communication is initiated after t_B-FREE.
This device does not support sequential register read/
write. Each register needs to be addressed using the
Register Pointer.
This device supports the Receive Protocol. The
register can be specified using the pointer for the initial
read. Each repeated read or receive begins with a Start
condition and address byte. The TCN75A retains the
previously selected register. Therefore, it outputs data
from the previously specified register (repeated pointer
specification is not necessary).
4.1.2 MASTER/SLAVE
The bus is controlled by a master device (typically a
microcontroller) that controls the bus access and
generates the Start and Stop conditions. The TCN75A
is a slave device and does not control other devices in
the bus. Both master and slave devices can operate as
either transmitter or receiver. However, the master
device determines which mode is activated.
4.1.3 START/STOP CONDITION
A high-to-low transition of the SDA line (while SCL is
high) is the Start condition. All data transfers must be
preceded by a Start condition from the master. If a Start
condition is generated during data transfer, the
TCN75A resets and accepts the new Start condition.
A low-to-high transition of the SDA line (while SCL is
high) signifies a Stop condition. If a Stop condition is
introduced during data transmission, the TCN75A
releases the bus. All data transfers are ended by a Stop
condition from the master.
4.1.4 ADDRESS BYTE
Following the Start condition, the host must transmit an
8-bit address byte to the TCN75A. The address for the
TCN75A Temperature Sensor is ‘1001,A2,A1,A0’ in
binary, where the A2, A1 and A0 bits are set externally
by connecting the corresponding pins to V_DD ‘1’ or
GND ‘0’. The 7-bit address transmitted in the serial bit
stream must match the selected address for the
TCN75A to respond with an ACK. Bit 8 in the address
byte is a read/write bit. Setting this bit to ‘1’ commands
a read operation, while ‘0’ commands a write operation
(see Figure 4-1).
 2010 Microchip Technology Inc.
DS21935D-page 11