lack the complex logic needed to be a bus master.

Upon receiving an ALERT_ interrupt signal, the host

master can broadcast a receive-byte transmission to

the alert-response slave address (0001 100). Following

such a broadcast, any slave device generating an

interrupt attempts to identify itself by putting its own

address on the bus.

The alert response can activate several different slave

devices simultaneously. If more than one slave

attempts to respond, bus arbitration rules apply, and

the device with the lower address code wins. The los-

ing device does not generate an acknowledge

response and continues to hold the ALERT_ line low

until cleared. Successful completion of the read alert-

response protocol clears the interrupt latch, provided

the condition that caused the alert no longer exists.

Overtemperature Limit Output

OVERT1 asserts when the temperature rises to a value

stored in one of the OVERT1 limit registers (19h and

20h). It deasserts when the temperature drops below

the stored limit, minus hysteresis. OVERT1 can be used

to activate a cooling fan, send a warning, invoke clock

throttling, or trigger a system shutdown to prevent com-

ponent damage.

Command-Byte Functions

The 8-bit command-byte register (Table 3) is the mas-

ter index that points to the various other registers within

the MAX6638. The register’s POR state is 0000 0000,

so a receive-byte transmission (a protocol that lacks

the command byte) that occurs immediately after POR

returns the current local-temperature data.

One-Shot Conversion Cycle

The one-shot command immediately forces a new con-

version cycle to begin. If the MAX6638 receives a one-

shot command while the MAX6638 is in standby mode

(RUN = 1), a new conversion begins, after which the

device returns to standby mode. If during a conversion

the MAX6638 receives a one-shot command, the

MAX6638 ignores the command; however, the results of

the conversion in progress update the data registers

accordingly.

Configuration-Byte Functions

The configuration-byte register (Tables 3 and 5) is a

read-write register with several functions. Bit 7 masks

interrupts. Bit 6 puts the MAX6638 into a standby (STOP)

mode or autonomous (RUN) mode. The MAX6638 enters

standby mode when both SMBus controllers set the cor-

responding configuration bits.

Status-Byte Functions

The status-byte register (Tables 3 and 4) indicates

when any temperature threshold is exceeded. This byte

also indicates whether the ADC is converting and if

there is a fault detected in the external sense diode.

After POR, the state of the flag bits are zero, assuming

no alarm conditions are present. The status byte clears

with any successful read of the status byte, after com-

pletion of a conversion and if the fault condition no

longer exists. Note that the ALERT_ interrupt latch does

not automatically clear when the status-flag bit indicat-

ing the ALERT_ clears.

Registers

The internal registers of the MAX6638 are all 8-bit data

word width and are all accessible through SMBus by

read and write operations.

Temperature Monitor with

Dual Serial Interface

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