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DS1726U+

P1-P3P4-P6P7-P9P10-P12
DS1626/DS1726
7 of 12
Table 2. 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.
DS1626/DS1726
8 of 12
CPU BIT AND STAND-ALONE THERMOSTAT OPERATION
In stand-alone thermostat mode, DS1626/DS1726 thermostat functionality can be used without requiring
a microcontroller to start/stop temperature conversions. The CPU bit in the configuration register
determines if stand-alone mode is enabled.
When CPU = 1 stand-alone mode is disabled, and the only way to start/stop temperature conversions is
by using a microcontroller to transmit Start Convert T and Stop Convert T commands, respectively.
Stand-alone mode is enabled when CPU = 0. In this mode, when RST = 0 the CLK/CNV pin operates as
a control signal to start and stop temperature measurements. Driving CLK/CNV low initiates continuous
temperature conversions that will continue until CLK/CNV is brought high again. If the CLK/CNV pin is
driven low and then returned to a high state in less than 10ms, only one temperature conversion will be
performed after which the DS1626/DS1726 will return to a low-power idle state (i.e., one-shot operation).
Note that when stand-alone mode is enabled, the 1SHOT bit in the configuration register is ignored, and
only the CLK/CNV signal determines whether continuous or one-shot conversions take place.
Since T
H
, T
L
, and the CPU bit are stored in EEPROM, the DS1626/DS1726 can be preprogrammed for
stand-alone operation. If desired, the CLK/CNV and RST pin can be connected to GND so the
DS1626/DS1726 will automatically begin taking temperature measurements at power-up
Normal bus communication with the DS1626/DS1726 can still take place in stand-alone mode when
RST = 1. When communication is initiated, stand-alone conversions are automatically halted. If during
the bus communication continuous temperature conversions are started using the Start Convert T
command, they can only be stopped by issuing a Stop Convert T command.
Figure 5. THERMOSTAT OUTPUT OPERATION
T
L
T
H
TEMP
LOGIC 0
LOGIC 1
T
COM
TEMP
LOGIC 0
LOGIC 1
T
HIGH
TEMP
LOGIC 0
LOGIC 1
T
LOW
DS1626/DS1726
9 of 12
CONFIGURATION REGISTER
The configuration register allows the user to customize the DS1626/DS1726 conversion and thermostat
options. It also provides information to the user about conversion status, EEPROM activity, and
thermostat activity. The configuration register is arranged as shown in Figure 6 and detailed descriptions
of each bit are provided in Table 3. This register can be accessed using the Read Config and Write Config
commands. Note that the R1, R0, CPU, and 1SHOT bits are stored in EEPROM and all other
configuration register bits are SRAM.
Figure 6. CONFIGURATION REGISTER
MSb BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 LSb
DONE THF TLF NVB R1* R0* CPU* 1SHOT*
*NV (EEPROM)
Table 3. CONFIGURATION REGISTER BIT DESCRIPTIONS
BIT NAME
(USER ACCESS)
FUNCTIONAL DESCRIPTION
DONE
(Read Only)
Power-up state = 1.
DONE = 0. Temperature conversion is in progress.
DONE = 1. Temperature conversion is complete.
THF
(Read/Write)
Power-up state = 0.
THF = 1. The measured temperature has reached or exceeded the value stored in the
T
H
register. THF will remain a 1 until it is overwritten with a 0 by the user, the
power is cycled, or a Software POR command is issued.
TLF
(Read/Write)
Power-up state = 0.
TLF = 1. The measured temperature has equaled or dropped below the value stored
in the T
L
register. TLF will remain a 1 until it is overwritten with a 0 by the user, the
power is cycled, or a Software POR command is issued.
NVB
(Read Only)
Power-up state = 0.
NVB = 1. Write to an E
2
memory cell is in progress.
NVB = 0. NV memory is not busy.
R1*
(Read/Write)
Power-up state = last value written to this bit.
Sets conversion resolution (see Table 4).
Initial state from factory = 1.
R0*
(Read/Write)
Power-up state = last value written to this bit.
Sets conversion resolution (see Table 4).
Initial state from factory = 1.
CPU*
(Read/Write)
Power-up state = last value written to this bit.
CPU = 1. Stand-alone mode is disabled.
CPU = 0. Stand-alone mode is enabled when RST = 0. See CPU BIT AND STAND-
ALONE THERMOSTAT OPERATION section for more information.
Initial state from factory = 0.
1SHOT*
(Read/Write)
Power-up state = last value written to this bit.
1SHOT = 1: One-Shot Mode. The Start Convert T command initiates a single
temperature conversion and then the device goes into a low-power standby state.
1SHOT = 0: Continuous Conversion Mode. The Start Convert T command initiates
continuous temperature conversions.
Initial state from factory = 0.
*NV (EEPROM)
P1-P3P4-P6P7-P9P10-P12

DS1726U+

Mfr. #:
Buy DS1726U+
Manufacturer:
Maxim Integrated
Description:
Board Mount Temperature Sensors Digital Thermometer & Thermostat
Lifecycle:
New from this manufacturer.
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