Philips Semiconductors

Product data sheet

NE1617A

Temperature monitor for microprocessor systems

2004 Oct 05

11

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 3. 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 3. 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

External and internal temperature registers

Results of temperature measurements after every ADC conversion

are stored in two registers: Internal Temp register (RIT) for internal

or local diode temperature, and External Temp register (RET) for

external or remote diode temperature. These registers can be only

read over the SMBus. The reading temperature data is in 2’s

complement binary form consisting of 7-bit data and 1-bit sign

(MSB), with each data count represents 1

°C, and the MSB bit is

transmitted first over the serial bus. The contents of those two

registers are updated upon completion of each ADC conversion.

Table 4 shows some values of the temperature and data.

Table 4. Temperature data format

(2’s complement)

TEMPERATURE (

°C)

DIGITAL OUTPUT (8 BITS)

+127

0 111 1111

+126

0 111 1110

+100

0 110 0100

+50

0 011 0010

+25

0 001 1001

+1

0 000 0001

0

0 000 0000

–1

1 111 1111

–25

1 110 0111

–50

1 100 1110

–65

1 011 1111

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. The

Table 5 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 (0.25Hz).

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

consumption, is increased with the conversion rate.

Table 5. Conversion rate control byte

DATA

CONVERSION

RATE (Hz)

AVERAGE

SUPPLY CURRENT

(

00h

0.0625

TBD

01h

0.125

TBD

02h

0.25

TBD

03h

0.5

TBD

04h

1

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 & 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.

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.