© 2005 Microchip Technology Inc.

DS21977B-page 9

MCP9805

4.1

Registers

The

MCP9805

has

several

registers

that

are

user-accessible. These registers include the Capability

register, Configuration register, Event Temperature

Upper-Boundary and Lower-Boundary Trip registers,

Critical Temperature Trip register, Temperature regis-

ter, Manufacturer Identification register and Device

Identification register.

The Temperature register is read-only, used to access

the ambient temperature data. The data is loaded in

Temperature Upper-Boundary and Lower-Boundary

Trip registers are read/writes. If the ambient tempera-

ture drifts beyond the user-specified limits, the

MCP9805 outputs a signal using the Event pin (refer to

Section 4.2.3 “Event Output Configuration”). In

addition, the Critical Temperature Trip register is used

to provide an additional critical temperature limit.

The Capability register is used to provide bits

describing the MCP9805’s capability in measurement

resolution, measurement range and device accuracy.

The device Configuration register provides access to

configure the MCP9805’s various features. These

registers are described in further detail in the following

sections.

The registers are accessed by sending a Register

Pointer to the MCP9805 using the serial interface. This

is an 8-bit write-only pointer. However, the three Least

Significant bits (3-LSbs) are used as pointers and all

unused bits (bits 7-3) need to be cleared or set to ‘0’.

Register 4-1 describes the pointer or the address of

each register.

REGISTER 4-1:

REGISTER ADDRESS POINTER (WRITE-ONLY)

W-0

W-0

W-0

W-0

W-0

W-0

W-0

W-0

00

0

0

0

P2

P1

P0

bit 7

bit 0

bit 7-3

Writable Bits: Write ‘0’

Bits 7-3 must always be cleared or written to ‘0’. This device has additional registers that are

reserved for test and calibration. If these registers are accessed, the device may not perform

according to the specification.

bit 2-0

Pointer Bits:

000

=

Capability register

001

=

Configuration register (CONFIG)

010

=

011

=

100

=

101

=

110

=

Manufacturer ID register

111

=

Device ID/Revision register

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

- n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown