The TMP144 uses a TI proprietary, one-wire UART-compatible communication protocol called SMAART Wire™.

The TMP144 has two dedicated pins for communication:TX and RX. Usually, these two pins are connected

internally and the signal on the RX propagates to the TX, unless the device must send data on the bus or during

address assignment and alert procedures.

The interface has built-in timeouts (typically 28 ms) that return the interface to a known state if communication is

disrupted.

7.5.1 Communication Protocol

bit (LSB) first. Each 8-bit word begins with a Start bit that is logic low, and ends with a Stop bit that is logic high.

By using a Start bit and Stop bit for each 8-bit word, the TMP144 can calibrate each word and keep synchronous

communication throughout the process.

1. The host sends a Start bit to start the communication process.

2. The host sends the calibration byte (55h) to allow the TMP144 to sync to the baud rate of the host.

3. The host sends a Stop bit after the calibration byte.

4. The host sends a second Start bit, followed by the command register byte and a Stop bit.

5. The host sends a third Start bit, followed by the data byte only for writes.

6. The host will send the data byte(s) if the instruction is a write command.

7. The host sends a Stop bit to finish the process.

Note

The device will break the chain and send the data byte(s) if the instruction sent in the command

register is a read command.

The sequence is shown in Figure 7-4.

S

1

0

1

0

1

0

1

0

P

S

C0 C1 C2 C3 C4 C5 C6 C7

P

S

D0 D1 D2 D3 D4 D5 D6 D7

P

S

D9

D8

D10 D11D12 D13D14 D15 P

Command with Address Pointer

Calibration Byte (55h)

Register Data (8-bit)

Register Data (8-bit)

S = Start condition of SMAART Wire¡ protocol

P = Stop condition of SMAART Wire¡ protocol

Figure 7-4. Generic Communication Write Bitstream

S

1

0

1

0

1

0

1

0

P

S

C0 C1 C2 C3 C4 C5 C6 C7

P

S

D0 D1 D2 D3 D4 D5 D6 D7

P

S

D9

D8

D10 D11 D12 D13 D14 D15 P

Driven by TMP144

1-bit default delay for

bus direction change

Command with Address Pointer

Calibration Byte (55h)

Register Data (8-bit)

Register Data (8-bit)

S = Start condition of SMAART Wire¡ protocol

P = Stop condition of SMAART Wire¡ protocol

Figure 7-5. Generic Communication Read Bitstream

The command byte is decoded by the TMP144 to determine the format of the subsequent communication

operation. Table 7-2 lists the command register byte values.

Table 7-2. Command Byte Value

COMMAND

OPERATION

COMMAND BYTE ENCODING

HEX VALUE

C7 (MSB)

C6

C5

C4

C3

C2

C1

C0 (LSB)

GLBL

IN3/ID3

IN2/ID2

IN1/ID1

IN0/ID0

P1

P0

R/W

Global software

reset

1

0

1

1

0

1

0

0

B4

Global

initialization

1

0

0

0

1

1

0

0

8C

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TMP144

SBOS891A – OCTOBER 2018 – REVISED FEBRUARY 2021

Copyright © 2021 Texas Instruments Incorporated

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