PRODUCT SPECIFICATION

FM75

REV. 1.0.5 10/2/03

7

Registers

The FM75 contains the following five registers:

1.

Command Register

2.

Temperature Register

3.

Configuration Register

4.

5.

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.

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-

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.

Figure 2. FM75 Register Hierarchy

Serial Interface

Command Register

1-byte Write Only

Temperature Register

2-byte Read Only

Command Reg. = 00000000

Configuration Register

1-byte Read/Write

Command Reg. = 00000001

2-byte Read/Write

Command Reg. = 00000010

2-byte Read/Write

Command Reg. = 00000011

Command

(‘Pointer’)

Data

Read/Write

Data

SDA

SCL

Figure 3. Command Register Format

Table 2. Register Assignments for Command

Bits P1 and P2

0

0

0

00

0

P1 P0

MSB

LSB

Register

P1

P0

Temperature Register

0

0

Configuration Register

0

1

1

0

1

1