ADT7483A

Rev. 1 | Page 13 of 24 | www.onsemi.com

Table 10. Conversion Rate/Channel Selector Register

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, hence, setting this bit has no effect).

Default = 0 = averaging 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.

01 = local temperature.

10 = Remote 1 temperature.

11 = Remote 2 temperature.

<3:0>

Conversion

Rates

These bits set how often the ADT7483A measures each temperature channel.

Conversions/second

Time (seconds)

0000 = 0.0625

16

0001 = 0.125

8

0010 = 0.25

4

0011 = 0.5

2

0100 = 1

1

0101 = 2

500 m

0110 = 4

250 m

0111 = 8 = default

125 m

1000 = 16

62.5 m

1001 = 32

31.25 m

1010 = continuous measurements

Limit Registers

The ADT7483A 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 over

the SMBus. See Table 8 for details of the limit registers’ addresses

and their power-on default values.

When Pin 13 is configured as an ALERT output, the high limit

registers perform a > comparison while the low limit registers

perform a ≤ comparison. For example, if the high limit register

is programmed with 80°C, then measuring 81°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 13 is configured as THERM2,

exceeding either the local limit 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 to any value after power-up using Register

Address 0x21.

It is important to remember that the data format for temperature

limits is the same as the temperature measurement data format.

Thus, if the temperature measurement uses the default (binary),

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.