Rainbow Electronics DS1775R_T - Manual (Page 4)

DS1775
4 of 13
table assumes the DS1775 is configured for 12–bit resolution; if the device is configured in a lower
resolution mode, those bits will contain zeros. The data is transmitted serially over the 2–wire serial
interface, MSb first. The MSb of the temperature register contains the “sign” (S) bit, denoting whether the
temperature is positive or negative. For Fahrenheit usage, a lookup table or conversion routine must be
used.
Temperature/Data Relationships Table 2
S 2
6
2
5
2
4
2
3
2
2
2
1
2
0
MSB
MSb (UNIT = °C) LSb
2 -1 2 -2 2 -3 2 -4 0 0 0 0 LSB
TEMP DIGITAL OUTPUT
(Binary)
DIGITAL OUTPUT (Hex)
+125 °C 0111 1101 0000 0000 7D00h
+25.0625 °C 0000 1010 0010 0000 1910h
+10.125 °C 0000 1010 0010 0000 0A20h
+0.5 °C 0000 0000 1000 0000 0080h
+0 °C 0000 0000 0000 0000 0000h
-0.5 °C 1111 1111 1000 0000 FF80h
-10.125 °C 1111 0101 1110 0000 F5E0h
-25.0625 °C 1110 0110 1111 0000 E6F0h
-55 °C 1100 1001 0000 0000 C900h
OPERATION–Thermostat Control
In its comparator operating mode, the DS1775 functions as a thermostat with programmable hysteresis, as
shown in Figure 2. When the DS1775’s temperature meets or exceeds the value stored in the high
temperature trip register (T
OS
) a consecutive number of times, as defined by the configuration register, the
output becomes active and stays active until the first time that the temperature falls below the temperature
stored in the low temperature trigger register (T
HYST
). In this way, any amount of hysteresis may be
obtained. The DS1775 powers up in the comparator mode with T
OS
=80 °C and T
HYST
=75 °C and can be
used as a standalone thermostat (no 2–wire interface required) with those setpoints.
In the interrupt mode, the O.S. output will first become active following the programmed number of
consecutive conversions above T
OS
. The fault can only be cleared by either setting the DS1775 in a
shutdown mode or by reading any register (temperature, configuration, T
OS
, or T
HYST
) on the device.
Following a clear, a subsequent fault can only occur if consecutive conversions fall below T
HYST
. This
interrupt/clear process is thus cyclical (T
OS
, clear, T
HYST
, clear, T
OS
, clear, T
HYST
, clear, ...). Only the first
of multiple consecutive T
OS
violations will activate O.S., even if each fault is separated by a clearing
function. The same situation applies to multiple consecutive T
HYST
events.