S

P

Calibration Byte (55h)

Command Phase

1

1

0

0

1

0

0

1

AC0

AC1

AC2 AC3 AC4

Address Assign Byte

A0

A1

A2

A3

A4

G/nI R/nW C/nA

Address Response Byte from Sensor 1

1

1

0

0

1

0

1

0

S

P

S

P

1

0

1

A0

A1

A2

A3

A4

7ms

7 ms

S

P

1

1

0

Address Response Byte from Sensor 2

S

P

1

0

1

A0

A1

A2

A3

A4

7ms

7 ms

Address Response Byte from Sensor N

S

P

1

0

1

A0

A1

A2

A3

A4

7ms

7 ms

TMP107

www.ti.com

SBOS716B – MAY 2015 – REVISED SEPTEMBER 2015

7.3.3.2 SMAART Wire Operations

This section describes various types of communication operations and is illustrated with timing diagrams. The

diagrams in this section are used only to understand functional aspects of the communication; for timing aspects,

see the Timing Requirements table. The color of the phases in Figure 23 through Figure 29 indicates the

direction of the communication. The communication phases marked in black indicate the host controller is driving

the bus. The communication phases marked in red indicate one of the devices in the daisy chain is responding to

the host by driving the bus. The device communicates to the host controller through intermediate devices. The

intermediate devices are automatically configured as buffers to allow data to pass through from the I/O2 pin to

the I/O1 pin, and vice versa.

7.3.3.2.1

Command Operations

7.3.3.2.1.1

Address Initialize

The address-initialize command initializes the addresses of the devices in the daisy chain. This command must

be performed one time because the addresses are stored in the devices EEPROM and loaded on every reset

event.

After the address-initialize command phase, the host provides one word of address-assign, command-byte data,

as shown in Figure 23. This word contains the desired address of the first device on the daisy chain in the A4:A0

field. Although any value from 0 to 31 is allowed for this field, it is recommended to keep first device address at

01h. The last device address must never exceed 31. After the address-assign command bytes have been

transmitted by the host, the daisy chain goes through a sequence of position detection and self-programming

events where the devices in the chain identify their respective locations on the bus. During this process, the host

receives incremental address response data from the individual TMP107 devices in the daisy chain that indicate

the point in the chain up to which the address assignment has been completed. These responses arrive at

intervals of 7 ms. This procedure is represented in Figure 23.

Figure 23. Address-Initialize Command

Until the initialization process is completed, daisy-chain communication is directed toward the host. Do not send

any new commands to the chain during this period. If the address initialization sequence is interrupted as a result

of glitches or disconnects in the daisy chain, the devices stall communication. In the event of a stall, each device

has an internal timeout of one second (only for the address-initialize command). After one second, the

communication interface in the TMP107 device resets, and the host regains control of the chain. Float the I/O2

pin of the last device in the chain. The address initialization procedure occurs serially from one device to the

next; therefore, the maximum current consumed by the chain must not exceed the current required to initialize

one device.

Copyright © 2015, Texas Instruments Incorporated

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