1.

Master Senses SMBus alert line low

2.

Master sends a START followed by the Alert Response

Address (ARA) with a Read Command.

3.

Alerting Device(s) send ACK.

4.

Alerting Device(s) send their Address. While transmitting

their address, alerting devices sense whether their ad-

dress has been transmitted correctly. (The LM86 will

reset its ALERT output and set the ALERT mask bit once

its complete address has been transmitted successfully.)

5.

Master/slave NoACK

6.

Master sends STOP

7.

Master attends to conditions that caused the ALERT to

be triggered. The STATUS REGISTER is read and fan

started, setpoint limits adjusted, etc.

8.

Master resets the ALERT mask (D7 in the Configuration

register).

The ARA, 000 1100, is a general call address. No device

should ever be assigned this address.

Bit D0 (the ALERT configure bit) in the FILTER and ALERT

CONFIGURE REGISTER (xBF) must be set low in order for

the LM86 to respond to the ARA command.

The ALERT output can be disabled by setting the ALERT

mask bit, D7, of the Configuration register. The power on

default is to have the ALERT mask bit and the ALERT

configure bit low.

1.3 T_CRIT_A OUTPUT and T_CRIT LIMIT

T_CRIT_A is activated when any temperature reading is

greater than the limit preset in the critical temperature set-

point register (T_CRIT), as shown in Figure 6. The Status

Register can be read to determine which event caused the

alarm. A bit in the Status Register is set high to indicate

which temperature reading exceeded the T_CRIT setpoint

temperature and caused the alarm, see Section 2.3.

Local and remote temperature diodes are sampled in se-

quence by the A/D converter. The T_CRIT_A output and the

Status Register flags are updated after every Local and

Remote temperature conversion. T_CRT_A follows the state

of the comparison, it is reset when the temperature falls

below the setpoint RCS-TH. The Status Register flags are

reset only after the Status Register is read and if a tempera-

ture conversion(s) is/are below the T_CRIT setpoint, as

shown in . Figure 6

1.4 POWER ON RESET DEFAULT STATES

LM86 always powers up to these known default states. The

LM86 remains in these states until after the first conversion.

1.

Command Register set to 00h

2.

Local Temperature set to 0˚C

3.

Remote Diode Temperature set to 0˚C until the end of

the first conversion.

4.

Status Register set to 00h.

5.

Configuration register set to 00h; ALERT enabled, Re-

mote T_CRIT alarm enabled and Local T_CRIT alarm

enabled

6.

85˚C Local and Remote T_CRIT temperature setpoints

7.

70˚C Local and Remote HIGH temperature setpoints

8.

0˚C Local and Remote LOW temperature setpoints

9.

Filter and Alert Configure Register set to 00h; filter dis-

abled, ALERT output set as an SMBus ALERT

10. Conversion Rate Register set to 8h; conversion rate set

to 16 conv./sec.

1.5 SMBus INTERFACE

The LM86 operates as a slave on the SMBus, so the

SMBCLK line is an input and the SMBData line is bi-

directional. The LM86 never drives the SMBCLK line and it

does not support clock stretching. According to SMBus

specifications, the LM86 has a 7-bit slave address. All bits A6

through A0 are internally programmed and can not be

changed by software or hardware.

The complete slave address is:

A6

A5

A4

A3

A2

A1

A0

1

00110

0

1.6 TEMPERATURE DATA FORMAT

Temperature data can only be read from the Local and

Remote Temperature

registers;

the

setpoint

registers

(T_CRIT, LOW, HIGH) are read/write.

Remote temperature data is represented by an 11-bit, two’s

complement word with an LSB (Least Significant Bit) equal

to 0.125˚C. The data format is a left justified 16-bit word

available in two 8-bit registers:

10130329

FIGURE 5. ALERT Output as an SMBus ALERT

Temperature Response Diagram

10130306

FIGURE 6. T_CRIT_A Temperature Response Diagram

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