MAX31865 データシートの表示（PDF） - Maxim Integrated

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MAX31865

RTD-to-Digital Converter

Maxim Integrated 

MAX31865

RTD-to-Digital Converter

Fault Threshold Registers (03h–06h)

The High Fault Threshold and Low Fault Threshold

registers select the trip thresholds for RTD fault detection.

The results of RTD conversions are compared with the

values in these registers to generate the “Fault” (D[7:6])

bits in the Fault Status register. The RTD Data Registers,

High Fault Threshold Registers, and Low Fault Threshold

Registers all have the same format.

The RTD High bit in the Fault Status Register is set if the

RTD resistance register value is greater than or equal to

the value in the High Fault Threshold register. The POR

value of the High Fault Threshold register is FFFFh.

The RTD Low bit in the Fault Status Register is set if the

RTD resistance value is less than or equal to the value in

the Low Fault Threshold register. The POR value of the

Low Fault Threshold register is 0000h.

Fault Status Register (07h)

The Fault Status register latches any detected fault bits;

writing a 1 to the Fault Status Clear bit in the Configuration

Register returns all fault status bits to 0.

Serial Interface

The MAX31865 supports SPI modes 1 and 3. Four pins

are used for SPI-compatible communications: SDO

(serial-data out), SDI (serial-data in), CS (chip select),

and SCLK (serial clock). SDI and SDO are the serial-

data input and output pins for the devices, respectively.

The CS input initiates and terminates a data transfer.

SCLK synchronizes data movement between the master

(microcontroller) and the slave (MAX31865).

The serial clock (SCLK), which is generated by the

microcontroller, is active only when CS is low and dur­

ing address and data transfer to any device on the

Table 6. Fault Threshold Registers Definition

REGISTER

Bit

RTD

Resistance

Data

HIGH FAULT THRESHOLD MSB (03h) REGISTER

LOW FAULT THRESHOLD MSB (05h) REGISTER

D7 D6 D5 D4 D3 D2 D1 D0

MSB — — — — — — —

Bit

Weighting

214

213

212

211

210

29

28

27

Decimal

Value

16384 8192 4096 2048 1024 512 256 128

X = Don’t care

HIGH FAULT THRESHOLD LSB (04h) REGISTER

LOW FAULT THRESHOLD MSB (06h) REGISTER

D7 D6 D5 D4 D3 D2 D1 D0

— — — — — — LSB X

26

25

24

23

22

21

20

—

64 32 16 8

4

2

1

—

Table 7. Fault Status Register Definition

D7

RTD High

Threshold

X = Don’t care

D6

RTD Low

Threshold

D5

REFIN- >

0.85 x VBIAS

D4

REFIN- < 0.85 x VBIAS

(FORCE- open)

D3

RTDIN- < 0.85 x

VBIAS (FORCE- open)

D2

Overvoltage/

undervoltage fault

D1 D0

xx

Maxim Integrated

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