FM75 Fairchild Semiconductor, FM75 Datasheet - Page 7

• Manufacturer Part Number: FM75
• Description: Low Voltage 2-Wire Digital Temperature Sensor with Thermal Alarm
• Manufacturer: Fairchild Semiconductor

PRODUCT SPECIFICATION
Registers
The FM75 contains the following five registers:
1. Command Register
2. Temperature Register
3. Configuration Register
4. Over-Limit-Signal Temperature Register (T
5. Hysteresis Temperature Register (T
All of these registers can be accessed by the user via the
digital serial interface at any time (see Serial Interface
Operation for instructions). A detailed description of these
registers and their functions is provided in the following
paragraphs. A diagram of the register hierarchy is shown in
Figure 2.
REV. 1.0.4 10/3/02
MSB
0
Figure 3. Command Register Format
0
0
Command Register
0
SDA
Serial Interface
1-byte Write Only
0
Command
0 P1 P0
(‘Pointer’)
HYST
Data
SCL
Figure 2. FM75 Register Hierarchy
)
LSB
OS
)
Read/Write
Data
Command Register
The Command Register is a one-byte (8-bit) write-only
register. The data stored in the Command Register indicates
which of the other four registers (Temperature, Configura-
tion, T
write to during an upcoming operation. In other words the
Command Register “points” to the selected register as shown
in Figure 2.
The Command Register is illustrated in Figure 3. The P1 and
P0 bits of the Command Register determine which register is
to be accessed as shown in Table 2. The six MSBs of the
Command Register must always be zero. Writing a 1 into
any of these bits will cause the current operation to be
terminated.
The Command Register retains pointer information between
operations. Therefore, this register only needs to be updated
once for consecutive read operations from the same register.
All bits in the Command Register default to zero at
power-up.
Table 2. Register Assignments for Command
Bits P1 and P2
Register
Temperature Register
Configuration Register
T
T
HYST
OS
OS
Register
Configuration Register
, or T
Register
Temperature Register
Command Reg. = 00000000
Command Reg. = 00000001
Command Reg. = 00000010
Command Reg. = 00000011
1-byte Read/Write
2-byte Read/Write
2-byte Read/Write
T
2-byte Read Only
HYST
T
HYST
OS
Register
) the user intends to read from or
Register
P1
0
0
1
1
P0
0
1
0
1
FM75
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