ADT7481

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10

Table 6. Conversion Rate/Channel Selector Register (Read Address 0x04, Write Address 0x0A)

Bit

Mnemonic

Function

7

Averaging

Setting this bit to 1 disables averaging of the temperature measurements at the slower conversion

rates (averaging cannot take place at the three faster rates, so setting this bit has no effect). When

default = 0, averaging is enabled.

6

Reserved

Reserved for future use. Do not write to this bit.

<5:4>

Channel Selector

These bits are used to select the temperature measurement channels:

00 = Round robin = default = all channels measured

01 = Local temperature only measured

10 = Remote 1 temperature only measured

11 = Remote 2 temperature only measured

<3:0>

Conversion Rates

These bits set how often the ADT7481 measures each temperature channel.

Conversion rates are as follows:

Conversions/sec

Time (seconds)

0000 = 0.0625

0001 = 0.125

0010 = 0.25

0011 = 0.5

0100 = 1

0101 = 2

0110 = 4

0111 = 8 = default

1000 = 16

1001 = 32

1010 = 64

1011 = continuous measurements

16

8

4

2

1

500 m

250 m

125 m

62.5 m

31.25 m

15.5 m

73 m (averaging enabled)

Limit Registers

The ADT7481 has three limits for each temperature

channel: high, low, and THERM temperature limits for

local, Remote 1, and Remote 2 temperature measurements.

The remote temperature high and low limits span two

registers each to contain an upper and lower byte for each

limit. There is also a THERM hysteresis register. All limit

registers can be written to, and read back from, the SMBus.

See Table 11 for details of the limit register addresses and

power−on default values.

C will result in an out−of−limit condition, setting a flag in

the status register.

If the low limit register is programmed with 0

°C,

measuring 0

°C or lower will result in an out−of−limit

condition.

Exceeding either the local or remote THERM limit asserts

THERM low. When Pin 8 is configured as THERM2,

exceeding either the local or remote high limit asserts

THERM2 low. A default hysteresis value of 10

°C is

provided that applies to both THERM channels. This

hysteresis value may be reprogrammed.

It is important to remember that the temperature limits

data format is the same as the temperature measurement data

format. So if the temperature measurement uses the default

binary scale, then the temperature limits also use the binary

scale. If the temperature measurement scale is switched,

however, the temperature limits do not automatically

switch.

The user must reprogram the limit registers to the desired

value in the correct data format. For example, if the remote

low limit is set at 10

°C and the default binary scale is being

used, the limit register value should be 0000 1010b. If the

scale is switched to offset binary, the value in the low

temperature limit register should be reprogrammed to be

0100 1010b.

Status Registers

The status registers are read−only registers, at Address

0x02 (Status Register 1) and Address 0x23 (Status

Register 2). They contain status information for the

ADT7481.

Table 7. Status Register 1 Bit Assignments

Bit

Mnemonic

Function

ALERT

7

BUSY

1 when ADC converting

No

6

LHIGH

(Note 1)

1 when local high

temperature limit tripped

Yes

5

LLOW

(Note 1)

1 when local low

temperature limit tripped

Yes

4

1 When Remote 1 High

Temperature Limit Tripped

Yes

3

R1LOW

(Note 1)

1 When Remote 1 Low

Temperature Limit Tripped

Yes

2

D1 OPEN

(Note 1)

1 When Remote 1 Sensor

Open Circuit

Yes

1

R1THRM1

1 when Remote1 THERM

Limit Tripped

No

0

LTHRM1

1 when local THERM Limit

Tripped

No

1. These flags stay high until the status register is read, or they

are reset by POR.