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NE1618

Temperature monitor for microprocessor systems

Philips Electronics 

Philips Semiconductors

Temperature monitor for microprocessor systems

Product data

NE1618

Configuration register

The configuration register is used to mask the Alert interrupt and/or

to put the device in software standby mode. Only two bits 6 and 7 of

this register are used as listed in Table 5. Bit 7 is used to mask the

device ALERT output from Alert interruption when this bit is set to 1,

and bit 6 is used to activate the standby software mode when this bit

is set to to 1.

This register can be written or read using the commands of registers

named WC and RC accordingly. Upon power-on reset (POR), both

bits are reset to zero.

Table 5. Configuration register bit assignments

BIT

NAME

POR

STATE

FUNCTION

7 (MSB)

MASK

0

Mask ALERT interrupt:

Interrupt is enabled when

this bit is LOW, and disabled

when this bit is HIGH.

6

RUN/STOP

0

Standby or run mode

control:

When LOW, running mode is

enabled. When HIGH,

standby mode is initiated.

5 to 0 RESERVED n/a n/a

Conversion rate register

The conversion rate register is used to store programmable

conversion data, which defines the time interval between

conversions in standard free-running auto-convert mode. Table 6

shows all applicable data and rates for the device. Only three LSB

bits of the register are used and other bits are reserved for future

use. This register can be written to and read back over the SMBus

using commands of the registers named WCR and RCR

respectively. The POR default conversion data is 02h.

Because of the timing asynchronization, when changing the

conversion rate from fast to slow, or vice versa, you may get an

invalid data for the external temp reading, and an Alert interruption

as well. Therefore, caution must be taken when doing a change of

conversion rate. Changing conversion should be done in one of the

following ways:

1. Apply this sequential operation:

a. Put the device into its standby mode (by setting bit6 of the

WC register).

b. Wait at least 750 ms (to ensure the current conversion if

there is one to be completed).

c. Change the conversion rate (by writing the conversion data

into the WCR register).

d. Put the device back into its normal mode (by clearing bit6 of

the WC register).

2. Writing the conversion data to the conversion register WCR

when the busy bit is off. The busy bit can be monitored by

reading the Status Register (SR) bit 7.

We suggest that method “1.” is preferred because it will provide the

correct temp data in a defined time. Releasing the device from

shutdown mode by clearing bit6 of the WC register also initiates a

new conversion, and all the register data will be updated at the end

of the conversion in 750 ms (max.) for slow rate, and 170 ms for fast

rate.

The device will be automatically put into the extended measurement

mode when the conversion rate data is less than or equal to 04h.

Otherwise, it will be in basic measurement mode for the remote

temp.

Notice that the average supply current, as well as the device power

consumption, is increased with the conversion rate.

Table 6. Conversion rate control byte

DATA

00h

CONVERSION

RATE (Hz)

0.06

AVERAGE

SUPPLY CURRENT

(µA Typ. @ VDD = 3.3 V)

TBD

01h

0.12

TBD

02h

0.22

TBD

03h

0.40

TBD

04h

0.70

TBD

05h

2

TBD

06h

4

TBD

07h

8

TBD

08h to FFh

Reserved

n/a

Temperature limit registers

The device has four registers to be used for storing programmable

temperature limits, including the high limit and the low limit for each

channel of the external and internal diodes. Data of the temperature

register (RIT and RET) for each channel are compared with the

contents of the temperature limit registers of the same channel,

resulting in alarm conditions. If measured temperature either equals

or exceeds the corresponding temperature limits, an Alert interrupt is

asserted and the corresponding flag bit in the status register is set.

The temperature limit registers can be written to and read back

using commands of registers named WIHL, WILL, WEHL, WELL,

RIHL, RILL, REHL, RELL accordingly. The POR default values are

+127 °C (0111 1111) for the HIGH limit and –55 °C (1100 1001) for

the LOW limit.

Notice that only the RET data is used in limit comparison and REET

data is ignored.

One-shot command

The one shot command is not actually a data register as such and a

write operation to it will initiate an ADC conversion. The send byte

format of the SMBus, as described later, with the use of OSHT

command (0Fh), is used for this writing operation. In normal

free-running-conversion operation mode of the device, a one-shot

command immediately forces a new conversion cycle to begin.

However, if a conversion is in progress when a one-shot command

is received, the command is ignored. In software standby mode, the

one-shot command generates a single conversion and comparison

cycle and then puts the device back in its standby mode after the

conversion. In hardware standby mode, the one shot is inhibited.

Notice that a one-shot command will clear the REET register and

set a basic measurement for that cycle.

2002 Jan 04

10

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