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TEMPERATURE REGISTER

COMMUNICATING WITH THE TMP121

0.25s

0.5s

50

µA (active)

20

µA (idle)

TMP121-EP

TMP123-EP

SGLS315 – SEPTEMBER 2005

APPLICATION INFORMATION (continued)

The temperature register of the TMP121 and TMP123 is a 16 bit, signed read-only register that stores the output

of the most recent conversion. Up to 16 bits can be read to obtain data and are described in Table 1. The first 13

bits are used to indicate temperature with bits D2 = 0 and D1, D0 in a high impedance state. Data format for

temperature is summarized in Table 2. Following power-up or reset, the temperature register reads 0

°C until the

first conversion is complete.

Table 1. Temperature Register

D15

D14

D13

D12

D11

D10

D9

D8

D7

D6

D5

D4

D3

D2

D1

D0

T12

T11

T10

T9

T8

T7

T6

T5

T4

T3

T2

T1

T0

0

Z

Z

Table 2. Temperature Data Format

TEMPERATURE

HEX

(

°C)

(BINARY)

150

0100 1011 0000 0000

4B00

125

0011 1110 1000 0000

3E80

25

0000 1100 1000 0000

0C80

0.0625

0000 0000 0000 1000

0008

0

0000 0000 0000 0000

0000

–0.0625

1111 1111 1111 1000

FFF8

–25

1111 0011 1000 0000

F380

–55

1110 0100 1000 0000

E480

(1)

The last two bits are high impedance and are shown as 00 in the table.

The TMP121 and TMP123 continuously convert temperatures to digital data while CS is high. CS must be high

for a minimum of one conversion time (320 ms max) to update the temperature data. Reading temperature data

from the TMP121 and TMP123 is initiated by pulling CS low, which causes any conversion in progress to

terminate, and places the device into analog shutdown. Quiescent current is reduced to 1

µA during analog

shutdown. Once CS is pulled low, temperature data from the last completed conversion prior to dropping CS is

latched into the shift register and clocked out at SO on the falling SCK edge. The 16-bit data word is clocked out

sign bit first, followed by the MSB. Any portion of the 16-bit word can be read before raising CS. The TMP121

and TMP123 typically require 0.25 s to complete a conversion and consume 50

µA of current during this period.

If CS is held high for longer than one conversion time period the TMP121 and TMP123 goes into idle mode for

0.25 s, requiring only 20

µA of current. A new conversion begins every 0.5 s. Figure 6 describes the conversion

timing for the TMP121 and TMP123.

Figure 6. Conversion Time and Period

The serial data of the TMP121 and TMP123 consists of 12-bit plus sign temperature data followed by a

confirmation bit and two high impedance bits. Data is transmitted in binary two's complement format. Figure 7

describes the output data of the TMP121 and TMP123.

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