MCP9800/1/2/3

DS21909B-page 10

 2004 Microchip Technology Inc.

4.3.1

AMBIENT TEMPERATURE

The MCP9800/1/2/3 has a 16-bit read-only ambient

temperature register

temperature data. This data is formatted in two’s

complement. The bit assignments, as well as the

corresponding resolution, is shown in the register

assignment below.

The refresh rate of this register depends on the

selected ADC resolution. It takes 30 ms (typ.) for 9-bit

data and 240 ms (typ.) for 12-bit data. Since this

register is double-buffered, the user can read the

register while the MCP9800/1/2/3 performs analog-to-

digital conversion in the background. The decimal code

to ambient temperature conversion is shown in

Equation 4-2:

EQUATION 4-2:

T

A

Code

2

n

×

=

Where:

n

= -1, -2, -3 and -4 for 9-bit, 10-bit, 11-bit

and 12-bit resolution, respectively

= Ambient Temperature (°C)

Code= MCP980X output in decimal

(Table 4-1)

REGISTER 4-2:

Upper Half:

R-0

R-0

R-0

R-0

R-0

R-0

R-0

R-0

Sign

bit 15

bit 8

Lower Half:

R-0

R-0

R-0

R-0

R-0

R-0

R-0

R-0

0

0

0

0

bit 7

bit 0

Note:

When the 9-bit, 10-bit or 11-bit resolutions are selected, bit 6, bit 7 or bit 8 will remain clear <0>,

respectively.

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

- n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

TABLE 4-1:

AMBIENT TEMPERATURE TO CODE CONVERSION

Ambient Temperature

Code

(°C)

9-Bit

10-Bit

11-Bit

12-Bit

Binary

Hexadecimal

Decimal

+125°C

0FA

250

+125

+25.4375°C

0001 1001 0uuu uuuu

032

50

+25

+0.5°C

0000 0000 1uuu uuuu

001

1

+0.5

+125°C

0111 1101 00uu uuuu

1F4

500

+125

+25.4375°C

0001 1001 01uu uuuu

065

101

+25.25

+0.25°C

0000 0000 01uu uuuu

001

1

+0.25

+125°C

0111 1101 000u uuuu

3E8

1000

+125

+25.4375°C

0001 1001 011u uuuu

0CB

203

+25.375

+0.125°C

0000 0000 001u uuuu

001

1

+0.125

+125°C

0111 1101 0000 uuuu

7D0

2000

+125

+25.4375°C

0001 1001 0111 uuuu

197

407

+25.4375

+0.0625°C

0000 0000 0001 uuuu

001

1

+0.0625

0°C

0000 0000 0000 uuuu

000

0

0

–0.0625°C

1111 1111 1111 uuuu

(

2)

001

(

3)

-1

-0.0625

–25.4375°C

1110 0110 1001 uuuu

197

-407

-25.4375

–55°C

1100 1001 0000 uuuu

370

-880

-55

Note

1:

‘u’ represents unused bits. The MCP9800/1/2/3 clears <0> the unused bits.

2:

This data is in two’s complement format, which indicates ambient temperature below 0°C.

3:

Negative temperature magnitude in Hexadecimal. This conversion is done by complimenting each binary bit and

adding 1.