register was previously selected by a Write Byte

instruction. Use caution when using the shorter proto-

cols in multimaster systems, as a second master could

overwrite the command byte without informing the first

master.

Read temperature data from the read internal tempera-

ture (00h) and read external temperature (01h) regis-

ters. The temperature data format for these registers is

8 bits for each channel, with the LSB representing +1°C

(Table 1).

Read the additional bits from the read extended tem-

perature byte register (10h, 11h), which extends the

data to 10 bits and the resolution to +0.25

°C per LSB

(Table 2).

When a conversion is complete, the main temperature

register and the extended temperature register are

updated.

Alarm Threshold Registers

Two registers store ALERT threshold values—one each

for the local and remote channels. If either measured

temperature equals or exceeds the corresponding

ALERT threshold value, the ALERT interrupt asserts

unless the ALERT bit is masked.

The power-on-reset (POR) state of the local ALERT

°C (0100 0110). The POR state of

°C (0111 1000).

Diode Fault Detection

A continuity fault detector at DXP detects an open cir-

or short circuit exists, the external temperature register

is loaded with 1111 1111 and status bit 2 (OPEN) of the

status byte is set to 1. Immediately after POR, the status

register indicates that no fault is present. If a fault is

present upon power-up, the fault is not indicated until

the end of the first conversion. Diode faults do not set

the ALERT output.

ALERT Interrupts

The ALERT interrupt occurs when the internal or external

temperature reading exceeds a high temperature limit

(user programmed). The ALERT interrupt output signal is

latched and can be cleared only by reading the status

register after the fault condition no longer exists or by

successfully responding to the alert response address. If

±1°C, SMBus-Compatible Remote/Local

Temperature Sensor with Overtemperature Alarm

_______________________________________________________________________________________

7

SMBCLK

AB

C

D

E

FG

H

I

SMBDATA

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

E = SLAVE PULLS SMBDATA LINE LOW

J

K

F = ACKNOWLEDGE BIT CLOCKED INTO MASTER

G = MSB OF DATA CLOCKED INTO MASTER

H = LSB OF DATA CLOCKED INTO MASTER

I = ACKNOWLEDGE CLOCK PULSE

J = STOP CONDITION

K = NEW START CONDITION

Figure 3. SMBus Read Timing Diagram

TEMP (

°C)

DIGITAL OUTPUT

130.00

1 000 0010

127.00

0 111 1111

126.00

0 111 1110

25

0 001 1001

0.00

0 000 0000

<0.00

0 000 0000

Diode fault (short or open)

1 111 1111

Table 1. Main Temperature Register

(High Byte) Data Format

FRACTIONAL TEMP (°C)

DIGITAL OUTPUT

0.000

00XX XXXX

0.250

01XX XXXX

0.500

10XX XXXX

0.750

11XX XXXX

Table 2. Extended Resolution

Temperature Register (Low Byte) Data

Format