Datasheet

One-ShotStartRegister
ConfigurationRegisters
StatusRegister
IdentificationRegisters
N-FactorCorrectionRegisters
ConversionRateRegister
LocalandRemoteTemperatureRegisters
SDA
SCL
PointerRegister
I/O
Control
Interface
SoftwareReset
TMP421
TMP422
TMP423
SBOS398C –JULY 2007–REVISED MAY 2012 www.ti.com
Standard Decimal to Binary Temperature Data
Both local and remote temperature data use two
Calculation Example
bytes for data storage. The high byte stores the
temperature with 1°C resolution. The second or low
For positive temperatures (for example, +20°C):
byte stores the decimal fraction value of the
(+20°C)/(+1°C/count) = 20 → 14h → 0001 0100
temperature and allows a higher measurement
Convert the number to binary code with 8-bit,
resolution, as shown in Table 2. The measurement
right-justified format, and MSB = '0' to denote a
resolution for the both the local and remote channels
positive sign.
is 0.0625°C, and is not adjustable.
+20°C is stored as 0001 0100 → 14h.
Table 2. Decimal Fraction Temperature Data
For negative temperatures (for example, –20°C):
Format (Local and Remote Temperature Low
(|–20|)/(+1°C/count) = 20 → 14h → 0001 0100
Bytes)
Generate the two's complement of a negative
TEMPERATURE REGISTER LOW BYTE VALUE
(0.0625°C RESOLUTION)(1)
number by complementing the absolute value
TEMP
binary number and adding 1.
(°C) STANDARD AND EXTENDED BINARY HEX
0 0000 0000 00
–20°C is stored as 1110 1100 → ECh.
0.0625 0001 0000 10
REGISTER INFORMATION
0.1250 0010 0000 20
0.1875 0011 0000 30
The TMP421/22/23 contain multiple registers for
0.2500 0100 0000 40
holding configuration information, temperature
0.3125 0101 0000 50
measurement results, and status information. These
0.3750 0110 0000 60 registers are described in Figure 14 and Table 3.
0.4375 0111 0000 70
POINTER REGISTER
0.5000 1000 0000 80
0.5625 1001 0000 90
Figure 14 shows the internal register structure of the
0.6250 1010 0000 A0
TMP421/22/23. The 8-bit Pointer Register is used to
0.6875 1011 0000 B0
address a given data register. The Pointer Register
identifies which of the data registers should respond
0.7500 1100 0000 C0
to a read or write command on the two-wire bus. This
0.8125 1101 0000 D0
register is set with every write command. A write
0.8750 1110 0000 E0
command must be issued to set the proper value in
0.9385 1111 0000 F0
the Pointer Register before executing a read
(1) Resolution is 0.0625°C/count. All possible values are shown.
command. Table 3 describes the pointer address of
the TMP421/22/23 registers. The power-on reset
Standard Binary to Decimal Temperature Data
(POR) value of the Pointer Register is 00h (0000
Calculation Example
0000b).
High byte conversion (for example, 0111 0011):
Convert the right-justified binary high byte to
hexadecimal.
From hexadecimal, multiply the first number by
16
0
= 1 and the second number by 16
1
= 16.
The sum equals the decimal equivalent.
0111 0011b → 73h → (3 × 16
0
) + (7 × 16
1
) = 115
Low byte conversion (for example, 0111 0000):
To convert the left-justified binary low-byte to
decimal, use bits 7 through 4 and ignore bits 3
through 0 because they do not affect the value of
the number.
0111b → (0 × 1/2)
1
+ (1 × 1/2)
2
+ (1 × 1/2)
3
+ (1
× 1/2)
4
= 0.4375
Figure 14. Internal Register Structure
Note that the final numerical result is the sum of the
high byte and low byte. In negative temperatures, the
unsigned low byte adds to the negative high byte to
result in a value less than the high byte (for instance,
–15 + 0.75 = –14.25, not –15.75).
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