DS75 Datasheet, PDF (5/13 Pages) Dallas Semiconductor – 2.Wire Thermal Watchdog

DS75
O.S. OUTPUT TRANSFER FUNCTION Figure 2
Regardless of the mode chosen, the O.S. output is open–drain and the active state is set in the configura-
tion register. The power–up default is active low. Refer to the “OPERATION–Programming” section for
instructions in adjusting the thermostat setpoints, thermostat mode, and O.S. active state.
OPERATION–Programming
There are three areas of interest in programming the DS75: Configuration register, T_OS register, and the
T_HYST register. All programming is done via the 2–wire interface by setting the pointer to the appropriate
location. Table 3 illustrates the pointer settings for the four registers of the DS75.
Pointer Register Structure Table 3
POINTER ACTIVE REGISTER
00h
Temperature (default)
01h
Configuration
02h
T_HYST
03h
T_OS
The DS75 will power up with the temperature register selected. If the host wishes to change the data
pointer, it simply addresses the DS75 in the write mode (R/W=0), receives an acknowledge, and writes
the 8 bits that correspond to the new desired location. The last pointer location is always maintained so
that consecutive reads from the same register do not require the host to always provide a pointer address.
The only exception is at power–up, in which case the pointer will always be set to 00h, the temperature
register. The pointer address must always proceed data in writing to a register, regardless of which
address is currently selected. Please refer to the “2–Wire Serial Data Bus” section for details of the 2–
wire bus protocol.
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