Datasheet

DS1720
6 of 14
THERMOSTAT OUTPUT OPERATION Figure 3
OPERATION AND CONTROL
The DS1720 must have temperature settings resident in the T
H
and T
L
registers for thermostatic operation.
A configuration/status register is also used to determine the method of operation that the DS1720 will use
in a particular application, as well as indicating the status of the temperature conversion operation. The
configuration register is defined as follows:
CONFIGURATION/STATUS REGISTER
DONE THF TLF NVB 1 0 CPU 1SHOT
where
DONE = Conversion Done bit. 1=conversion complete, 0=conversion in progress.
T
HF
= Temperature High Flag. This bit will be set to 1 when the temperature is greater than or equal to
the value of T
H
. It will remain 1 until reset by writing 0 into this location or by removing power from the
device. This feature provides a method of determining if the DS1720 has ever been subjected to
temperatures above T
H
while power has been applied.
T
LF
= Temperature Low Flag. This bit will be set to 1 when the temperature is less than or equal to the
value of T
L
. It will remain 1 until reset by writing 0 into this location or by removing power from the
device. This feature provides a method of determining if the DS1720 has ever been subjected to
temperatures below T
L
while power has been applied.
NVB = Nonvolatile Memory Busy Flag. 1=write to an E
2
memory cell in progress. 0=nonvolatile
memory is not busy. A copy to E
2
may take up to 10 ms.
CPU = CPU use bit. If CPU=0, the CLK/CONV pin acts as a conversion start control, when RST is low.
If CPU is 1, the DS1720 will be used with a CPU communicating to it over the 3–wire port, and the
operation of the CLK/
CONV pin is as a normal clock in concert with DQ and RST . This bit is stored in
nonvolatile E
2
memory, capable of at least 50,000 writes. The DS1720 is shipped with CPU=0.
1SHOT = One–Shot Mode. If 1SHOT is 1, the DS1720 will perform one temperature conversion upon
reception of the Start Convert T protocol. If 1SHOT is 0, the DS1720 will continuously perform
temperature conversion. This bit is stored in nonvolatile E 2 memory, capable of at least 50,000 writes.
The DS1720 is shipped with 1SHOT=0.