DS1626 Datasheet, PDF (7/13 Pages) Dallas Semiconductor – High-Precision 3-Wire Digital Thermometer and Thermostat

DS1626/DS1726
Table 4. 12-BIT RESOLUTION TEMPERATURE/DATA RELATIONSHIP
TEMPERATURE
(°C)
DIGITAL OUTPUT
(BINARY)
DIGITAL OUTPUT
(HEX)
+125
0111 1101 0000
7D0h
+25.0625
0001 1001 0001
191h
+10.125
0000 1010 0010
0A2h
+0.5
0000 0000 1000
008h
0
0000 0000 0000
000h
-0.5
1111 1111 1000
FF8h
-10.125
1111 0101 1110
F5Eh
-25.0625
1110 0110 1111
E6Fh
-55
1100 1001 0000
C90h
OPERATION—THERMOSTAT FUNCTION
The DS1626/DS1726 thermostat outputs (T_HIGH, T_LOW, and T_COM) are updated after every temperature
conversion and remain at the updated values until the next conversion completes. T_HIGH is asserted
when the measured temperature is higher than or equal to the value stored in the T_H register, and T_LOW
is asserted when the temperature is equal to or falls below the value in the T_L register (see Figure 5).
T_COM uses both T_H and T_L to provide programmable hysteresis: when the measured temperature equals
or exceeds T_H, T_COM is asserted and it remains asserted until the temperature falls to a value equal to or
below T_L. All three thermostat outputs are active-high outputs.
The Write TH and Write TL commands are used to program the 12-bit T_H and T_L registers with user-
defined two’s complement values. The MSb (bit 11) of each register contains the two’s complement
sign bit (S). For the T_COM thermostat output to function correctly, the T_L value must be less than the T_H
value. Any unused LSbs in the T_H and T_L registers are forced to 0 regardless of the data written to
those bits. The unused LSbs are determined by the conversion resolution set by R1 and R0 in the
configuration register. Therefore, for 9-bit conversions bits 2 through 0 will be 0, for 10-bit
conversions bit 1 and bit 0 will be 0, and for 11-bit conversions bit 0 will be 0. All bits are used for 12-
bit conversions, so no bits are forced to 0. However, regardless of the conversion resolution, when
writing to T_H or T_L at least 12 bits must be sent following the Write TH or Write TL commands. The
reason is that data written to T_H and T_L is not saved to EEPROM until the DS1626/DS1726 have
received 12 bits, so if the operation is terminated before 12 bits have been received, the data will be
lost. Any additional bits sent after the first twelve are ignored (e.g., if two 8-bit words are written).
Another DS1626/DS1726 thermostat feature is the temperature-high flag (THF) and temperature-low
flag (TLF) in the configuration register. These bits provide a record of whether the temperature has
been greater than or equal to T_H or less than or equal to T_L at any time since the DS1626/DS1726 were
powered up. If the temperature is greater than or equal to the T_H register value, the THF bit in the
configuration register will be set to 1. If the temperature is less than or equal to the T_L register value,
the TLF bit in the configuration register will be set to 1. Once THF and/or TLF has been set, it will
remain set until the user overwrites it with a 0 or until the power is cycled.
7 of 13