DS1621
Higher resolutions may be obtained by reading the temperature and truncating the 0.5° bit (the LSB)
C
from the read value. This value is TEMP_READ. The value left in the counter may then be read by
issuing a READ COUNTER command. This value is the count remaining (COUNT_REMAIN) after the
gate period has ceased. By loading the value of the slope accumulator into the count register (using the
READ SLOPE command), this value may then be read, yielding the number of counts per degree C
(COUNT_PER_C) at that temperature. The actual temperature may be then be calculated by the user
using the following:
TEMPERATURE=TEMP_READ-0.25 +
(
COUNT
_
PER
_
C
−
COUNT
_
REMAIN
)
COUNT
_
PER
_
C
Thermostat Control
In its operating mode, the DS1621 functions as a thermostat with programmable hysteresis as shown in
Figure 3. The thermostat output updates as soon as a temperature conversion is complete.
When the DS1621’ temperature meets or exceeds the value stored in the high temperature trip register
s
(TH), the output becomes active and will stay active until the temperature falls below the temperature
stored in the low temperature trigger register (TL). In this way, any amount of hysteresis may be
obtained.
The active state for the output is programmable by the user so that an active state may either be a logic
"1" (V
DD
) or a logic "0" (0V).
THERMOSTAT OUTPUT OPERATION
Figure 3
DQ (Thermostat output, Active=High)
TL
TH
T (°C)
OPERATION AND CONTROL
The DS1621 must have temperature settings resident in the TH and TL registers for thermostatic
operation. A configuration/status register also determines the method of operation that the DS1621 will
use in a particular application, as well as indicating the status of the temperature conversion operation.
The configuration register is defined as follows:
DONE
THF
TLF
NVB
1
0
POL
1SHOT
where
DONE = Conversion Done bit. “1” = Conversion complete, “0” = Conversion in progress.
5 of 16
102299
DALLAS [ DALLAS SEMICONDUCTOR ]
