Philips Semiconductors

Product data

NE1618

Temperature monitor for microprocessor systems

2002 Jan 04

8

Table 2. Register assignments

REGISTER NAME

COMMAND BYTE

POR STATE

FUNCTION

RDID

FEH

N/A

Read device ID

RDRV

FFH

N/A

Read device revision

RIT

00H

0000 0000

Read internal or local temp

RET

01H

0000 0000

Read external or remote temp

REET

10H

0000 0000

Read extended external temp

RS

02H

N/A

Read status

RC

03H

0000 0000

Read configuration

RCR

04H

0000 0010

Read conversion rate

RIHL

05H

0111 1111

Read internal temp HIGH limit

RILL

06H

1100 1001

Read internal tem low limit

REHL

07H

0111 1111

Read external temp HIGH limit

RELL

08H

1100 1001

Read external temp LOW limit

WC

09H

N/A

Write configuration

WCR

0AH

N/A

Write conversion rate

WIHL

0BH

N/A

Write internal temp HIGH limit

WILL

0Ch

N/A

Write internal temp LOW limit

WEHL

0Dh

N/A

Write external temp HIGH limit

WELL

0Eh

N/A

Write external temp LOW limit

OSHT

0Fh

N/A

One shot command

RESERVED

11H

N/A

Reserved

RESERVED

12H

N/A

Reserved

RESERVED

13H

N/A

Reserved

RESERVED

14H

N/A

Reserved

RESERVED

15H

N/A

Reserved

Power-on reset (POR)

When the power is applied to the NE1618 while the device STDBY

input pin is at low state, the device will enter into its power–on reset

state and its registers are reset to their default values as shown in

the Table 2 resulting in:

ALERT pin is pulled to HIGH by an external pull-up resister.

–55

°C for low limit.

Notice that the content of the register that has indeterminate default

value will be unknown.

During the POR state of the device, the on-board A-to-D converter is

disabled and the measurement function of the device is inactive.

However, the SMBus interface is alive to bus communication

meaning that reading and writing the registers can be performed. If

there is no SMBus activity then the device will draw a small power

supply current less than 10

µA. Writing temp limits into the limits

registers if needed should usually be performed at this stage.

Starting conversion

Upon POR, if the STDBY input pin is set to HIGH while the

RUN/STOP bit 6 of the configuration register is equal to zero as

default, then the device will enter into its free-running operation

mode in which the device A-to-D converter is enabled and the

measurement function is activated. In this mode, the device cycles

the measurements of local temp and remote temp automatically and

periodically. The conversion period is defined by the programmable

conversion rate stored in the conversion register. It also performs

comparisons between readings and limits of the temperature in

order to set the flags and interruption accordingly at the end of every

conversion. Measured values are stored in the temp registers,

results of limit comparisons are reflected by the status of the flag

bits in the status register and interruption is reflected by the logical

level of the ALERT output pin. Temp and status data can be read at

any time. Temp limit values should be written into the limit registers

before starting conversion to avoid false conditions of the status.

Low power standby modes

The device can be put into one of the two standby modes from the

free-running state at any time: hardware standby mode by setting

the STDBY input pin to LOW, or software standby mode by setting

the RUN/STOP bit 6 of the configuration register to 1. In either

standby mode, the free-running operation is stopped, the supply

current is reduced to less than 10

µa if there is no SMBus activity, all

data in the device registers are retained. However, the SMBus is still

active and reading or writing registers can still be performed. The

main difference between the two standby modes is related to the

activation of the A-to-D conversion: data conversion can be

activated in the software standby mode but not in the hardware

standby mode. In software standby mode, an one-shot command

will initiate a single conversion which has the same effect in

comparing with any conversion that occurs when the device is in its