2005-2013 Microchip Technology Inc. DS21977C-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
parallel to this register after t
CONV
. The Event
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
0000 0P2 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 = Event Temperature Upper-Boundary Trip register (T
UPPER
)
011 = Event Temperature Lower-Boundary Trip register (T
LOWER
)
100 = Critical Temperature Trip register (T
CRIT
)
101 = Temperature register (T
A
)
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
