LTC2995 datasheet(83/90 Pages) AD

83 / 90 page

LTM2985

Rev. 0

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CUSTOM RTDS

convention shown in Table 94, where the first 14 bits

are the integer part and the remaining 10 bits are the

fractional part.

In this example, a custom RTD tied to CH3/CH4, with a

sense resistor on CH1/CH2, is programmed with the chan-

nel assignment data shown in Table 95 (refer to Figure 18

for a similar format). In this case, the custom data begins

at memory location 0x28C (starting address is 10). The

starting address (offset from 0x250) is entered in the

custom RTD data pointer field of the channel assignment

data. The table data length –1 (9 in this case) is entered

into the custom RTD data length field of the channel as-

signment word. Refer to Table 91 where the total number

of paired entries is 10.

Table 94. Example RTD Temperature Values

BYTE 1

BYTE 2

BYTE 3

B23 B22 B21 B20 B19 B18 B17 B16 B15 B14 B13 B12 B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

Temperature 213 212 211 210 29

20 2–1 2–2 2–3 2–4 2–5 2–6 2–7 2–8 2–9 2–10

112.3 0

200.56 0

273.16 0

377.25 0

489.66 0

595.22 0

697.87 0

765.14 0

801.22 0

900.5 0

Table 95. Custom RTD Channel Assignment Data

CONFIGURATION

FIELD

DESCRIPTION # BITS

BINARY

DATA

MEMORY

ADDRESS 0x20C

MEMORY

ADDRESS 0x20D

MEMORY

ADDRESS 0x20E

MEMORY

ADDRESS 0x20F

(1) RTD Type

Custom

10010 1 0 0 1 0

(2) Sense Resistor

Channel Pointer

CH2

00010

0 0 0 1 0

(3) Sensor

Configuration

4-Wire, No

Rotate, No Share

1000

1 0 0 0

(4) Excitation Current

25µA

0011

0 0 1 1

(5) Curve

Not Used for

Custom

0 0

(6) Custom RTD Data

Pointer

Start Address

= 10

001010

0 0 1 0 1 0

(7) Custom RTD Data

Length-1

Data Length –1

= 9

10 Paired Entries

001001

0 0 1 0 0 1

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