5.1 Registers

The MCP9808 has several registers that are user-accessible. These registers include the Temperature register, Configuration register, Temperature Alert Upper Boundary and Lower Boundary Limit registers, Critical Temperature Limit register, Manufacturer Identification register and Device Identification register.

The Temperature register is read-only, used to access the ambient temperature data. This register is double-buffered and it is updated every t_CONV. The Temperature Alert Upper Boundary and Lower Boundary Limit registers are read/write registers. If the ambient temperature drifts beyond the user-specified limits, the MCP9808 outputs a signal using the Alert pin (refer to Alert Output Configuration). In addition, the Critical Temperature Limit register is used to provide an additional critical temperature limit.

The Configuration register provides access to configure the MCP9808 device’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 MCP9808, using the serial interface. This is an 8-bit write-only pointer. However, the four Least Significant bits are used as pointers and all unused bits (Register Pointer<7:4>) need to be cleared or set to ‘0’. Table 5-1 describes the pointer or the address of each register.

Table 5-1. Register Pointer (Write-Only)
W-0	W-0	W-0	W-0	W-0	W-0	W-0	W-0
—	—	—	—	Pointer bits
bit 7							bit 0


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

7-4	W: Writable bits Write ‘`0`’. Bits 7-4 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.
3-0	Pointer bits `0000` = RFU, Reserved for Future Use (Read-Only register) `0001` = Configuration register (CONFIG) `0010` = Alert Temperature Upper Boundary Trip register (T_UPPER) `0011` = Alert Temperature Lower Boundary Trip register (T_LOWER) `0100` = Critical Temperature Trip register (T_CRIT) `0101` = Temperature register (T_A) `0110` = Manufacturer ID register `0111` = Device ID/Revision register `1000` = Resolution register `1xxx` = Reserved⁽1⁾

Note: Some registers contain calibration codes and should not be accessed.

Table 5-2. Bit Assignment Summary For All Registers (see Summary of Power-on Default For Power-on Defaults)
Register Pointer (Hex)	MSB/ LSB	Bit Assignment
Register Pointer (Hex)	MSB/ LSB	7	6	5	4	3	2	1	0
0x00	MSB	0	0	0	0	0	0	0	0
0x00	LSB	0	0	0	1	1	1	1	1
0x01	MSB	0	0	0	0	0	Hysteresis		SHDN
0x01	LSB	Crt Loc	Win Loc	Int Clr	Alt Stat	Alt Cnt	Alt Sel	Alt Pol	Alt Mod
0x02	MSB	0	0	0	SIGN	2⁷°C	2⁶°C	2⁵°C	2⁴°C
0x02	LSB	2³°C	2²°C	2¹°C	2⁰°C	2^-1°C	2^-2°C	0	0
0x03	MSB	0	0	0	SIGN	2⁷°C	2⁶°C	2⁵°C	2⁴°C
0x03	LSB	2³°C	2²°C	2¹°C	2⁰°C	2^-1°C	2^-2°C	0	0
0x04	MSB	0	0	0	SIGN	2⁷°C	2⁶°C	2⁵°C	2⁴°C
0x04	LSB	2³°C	2²°C	2¹°C	2⁰°C	2^-1°C	2^-2°C	0	0
0x05	MSB	T_A≥ T_CRIT	T_A> T_UPPER	T_A< T_LOWER	SIGN	2⁷°C	2⁶°C	2⁵°C	2⁴°C
0x05	LSB	2³°C	2²°C	2¹°C	2⁰°C	2^-1°C	2^-2°C	2^-3°C	2-4°C
0x06	MSB	0	0	0	0	0	0	0	0
0x06	LSB	0	1	0	1	0	1	0	0
0x07	MSB	0	0	0	0	0	1	0	0
0x07	LSB	0	0	0	0	0	0	0	0
0x08	LSB	0	0	0	0	0	0	1	1

MCP9808 DEMO CONTENT

5.1 Registers