Serial-to-Parallel/Parallel-to-Serial Converters and

Load-Switch Controllers with SMBus Interface

8

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and with the software START-STOP method (software

interrupts are discussed in the

START-STOP Software

Interrupt section). The I/O interrupts can be masked

individually. In addition, the software START-STOP

interrupt can be masked independently. The power-on-

reset state masks the START-STOP interrupt, as well as

the individual I/O interrupts to the ALERT pin (Table 1).

The thermal-shutdown interrupt cannot be masked.

Note that excessive noise on the supply can cause

false interrupts (see

Applications Information).

The MAX1661/MAX1662/MAX1663 are slave-only

devices that never initiate communications, except

when asserting an interrupt by forcing ALERT low, or

via the software START-STOP interrupt.

Alert Response Address (0001100)

The Alert Response (interrupt pointer) address pro-

vides quick fault identification for simple slave devices

that lack the complex, expensive logic needed to be a

bus master. When a slave device generates an inter-

Receive-Byte Format

ADDRESS

READ

ACK

DATA

ACK

START

CONDITION

7 bits

1 bit

(high)

1 bit

(low)

8 bits

1 bit

(high-Z)

STOP

CONDITION

ACK = SMBDATA High

Shaded = Slave Transmission

SMBCLK

A = START CONDITION

B = MSB OF ADDRESS CLOCKED INTO SLAVE

C = LSB OF ADDRESS CLOCKED INTO SLAVE

D = R/W BIT CLOCKED INTO SLAVE

A

B

C

D

E

F

G

H

I

J

SMBDATA

K

E = SLAVE PULLS SMBDATA LINE LOW

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 2b. SMBus Receive-Byte Timing Diagram and Format

Table 3. Format for Receive-Byte Data

BIT

NAME

POR STATE

FUNCTION

LATCHED

7 (MSB)

—

0

Not used

—

6

—

0

Not used

—

5

—

0

Not used

—

4

—

0

Not used

—

3

THSD

N/A

This bit indicates a thermal shutdown.

Yes

2

Data 3

N/A

This bit indicates the state of I/O3 (high or low).

No

1

Data 2

N/A

This bit indicates the state of I/O2 (high or low).

No

0

Data 1

N/A

This bit indicates the state of I/O1 (high or low).

No