Rainbow Electronics DS7505 - Manual (Page 5)

DS7505
Digital Thermometer and Thermostat
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Bit 15 Bit 14 Bit 13 Bit 12 Bit 11 Bit 10 Bit 9 Bit 8
MS Byte S 2 6 2 5 2 4 2 3 2 2 2 1 2 0
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
LS Byte 2 -1 2 -2 2 -3 2 -4 0 0 0 0
Figure 3. Temperature, T OS , and T HYST Register Format
Table 1. 12-Bit Resolution Temperature/Data Relationship
Operation
⎯Measuring
Temperature
The DS7505 measures temperature using a bandgap
temperature-sensing architecture. An on-board delta-
sigma analog-to-digital converter (ADC) converts the
measured temperature to a digital value that is calibrat-
ed in degrees Celsius; for Fahrenheit applications a
lookup table or conversion routine must be used. The
DS7505 is factory-calibrated and requires no external
components to measure temperature.
The DS7505 can be configured to power up either
automatically converting temperature or in a low-power
standby state. The preferred power-up mode can be
set using the SD bit in the configuration register as
explained in the
Configuration Register section. The
resolution of the digital output data is user-configurable
to 9, 10, 11, or 12 bits, corresponding to temperature
increments of 0.5
°C, 0.25°C, 0.125°C, and 0.0625°C,
respectively. The factory default resolution at power-up
is 9 bits (R1 = 0, R0 = 0), however this can be pro-
grammed to 10, 11, or 12 bits using the R0 and R1 bits
in the configuration register as explained in the
Configuration Register section. Note that the conver-
sion time doubles for each additional bit of resolution.
After each temperature measurement and analog-to-
digital (A/D) conversion, the DS7505 stores the temper-
ature as a 16-bit two’s complement number in the
2-byte temperature register (see Figure 3). The sign bit
(S) indicates if the temperature is positive or negative:
for positive numbers S = 0 and for negative numbers S
= 1. The most recently converted digital measurement
can be read from the temperature register at any time.
Since temperature conversions are performed in the
background, reading the temperature register does not
affect the operation in progress.
Bits 3 through 0 of the temperature register are hard-
wired to 0. When the DS7505 is configured for 12-bit
resolution, the 12 MSBs (bits 15 through 4) of the tem-
perature register contain temperature data. For 11-bit
resolution, the 11 MSBs (bits 15 through 5) of the tem-
perature register contain data, and bit 4 reads out as 0.
Likewise, for 10-bit resolution, the 10 MSBs (bits 15
through 6) contain data, and for 9-bit the 9 MSBs (bits
15 through 7) contain data and all unused LSBs con-
tains 0s. Table 1 gives examples of 12-bit resolution dig-
ital output data and the corresponding temperatures.
TEMPERATURE (
°C)
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX)
+125 0111 1101 0000 0000 7D00
+25.0625 0001 1001 0001 0000 1910
+10.125 0000 1010 0010 0000 0A20
+0.5 0000 0000 1000 0000 0080
0 0000 0000 0000 0000 0000
-0.5 1111 1111 1000 0000 FF80
-10.125 1111 0101 1110 0000 F5E0
-25.0625 1110 0110 1111 0000 E6F0
-55 1100 1001 0000 0000 C900