SMBus Digital Interface

From a software perspective, the MAX6622 appears as

a series of 8-bit registers that contain temperature mea-

surement data, alarm threshold values, and control bits.

A standard SMBus-compatible, 2-wire serial interface is

used to read temperature data and write control bits

and alarm threshold data. The same SMBus slave

address also provides access to all functions.

The MAX6622 employs four standard SMBus protocols:

write byte, read byte, send byte, and receive byte

(Figure 2). The shorter receive byte protocol allows

quicker transfers, provided that the correct data regis-

ter was previously selected by a read byte instruction.

Use caution with the shorter protocols in multimaster

systems, since a second master could overwrite the

command byte without informing the first master. Figure

3 is the SMBus write timing diagram and Figure 4 is the

SMBus read timing diagram.

The remote diode 1 measurement channel provides 11

bits of data (1 LSB = +0.125°C). All other temperature-

measurement channels provide 8 bits of temperature

data (1 LSB = +1°C). The 8 most significant bits (MSBs)

can be read from the local temperature and remote

temperature registers. The remaining 3 bits for remote

diode 1 can be read from the extended temperature

register. If extended resolution is desired, the extended

resolution register should be read first. This prevents

the most significant bits from being overwritten by new

5-Channel Precision Temperature Monitor

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7

Figure 1. Internal Block Diagram

DXP1

DXN1

DXP2

DXN2

DXP3

DXN3

DXP4

DXN4

INPUT

BUFFER

10/100

μA

REF

COUNT

COUNTER

COMMAND BYTE

REMOTE TEMPERATURES

LOCAL TEMPERATURES

REGISTER BANK

ALERT THRESHOLD

OVERT THRESHOLD

ALERT RESPONSE ADDRESS

ALARM

ALU

ADC

SMBus

INTERFACE

MAX6622

SMBCLK

SMBDATA

OVERT

AVERT

STBY