Rainbow-electronics DS1857 Instrukcja Użytkownika Pobierz pdf (Strona 9)

DS1857

Dual Temperature-Controlled Resistors with

External Temperature Input and Monitors

_____________________________________________________________________ 9

Monitored Signals

Each signal (V

, MON1, MON2, and temperature) is

available as a 16-bit value with 12-bit accuracy (left-jus-

tified) over the serial bus. See Table 1 for signal scales

and Table 2 for signal format. The four LSBs should be

masked when calculating the value.

The signals are updated every frame rate (t

frame

) in a

round-robin fashion.

The comparison of all four signals with the high and low

user-defined values are done automatically. The corre-

sponding flags are set to 1 within a specified time of

the occurrence of an out-of-limit condition.

Calculating Signal Values

The LSB = 100µV for V

, and the LSB = 38.147µV for

the MON signals.

To calculate the value of V

, convert the unsigned 16-

bit value to decimal and multiply by 100µV.

To calculate the value of MON1 or MON2, convert the

unsigned 16-bit value to decimal and multiply by

38.147µV.

To calculate the value of the temperature, treat the

two’s complement value binary number as an unsigned

binary number, then convert to decimal and divide by

256. If the result is greater than or equal to 128, then

subtract 256 from the result.

Temperature: high byte: -128°C to +127°C signed; low

byte: 1/256°C.

SIGNAL

+FS

SIGNAL

+FS

(hex)

-FS

SIGNAL

-FS

(hex)

Temperature

127.996°C 7FFF

-128°C 8000

6.55V

FFFF

0V 0000

MON1 2.5V

FFFF

0V 0000

MON2 2.5V

FFFF

0V 0000

Table 1. Scales for Monitor Channels

SIGNAL FORMAT

Unsigned

MON1 Unsigned

MON2 Unsigned

Temperature Two’s complement

Table 2. Signal Comparison

TEMPERATURE

CORRESPONDING LOOK-UP

TABLE ADDRESS

<-40°C 80h

-40°C 80h

-38°C 81h

-36°C 82h

-34°C 83h

——

+98°C C5h

+100°C C6h

+102°C C7h

>+102°C C7h

Table 3. Look-up Table Address for

Corresponding Temperature Values

MSB

LSB 2

MSB (BIN) LSB (BIN) VOLTAGE (V)

10000000 10000000 3.29

11000000 11111000 4.94

-1

-2

-3

-4

-5

-6

-7

-8

MSB (BIN) LSB (BIN) TEMPERATURE (°C)

01000000 00000000 64

01000000 00001111 64.059

01011111 00000000 95

11110110 00000000 -10

11011000 00000000 -40

MSB (BIN) LSB (BIN) VOLTAGE (V)

11000000 00000000 1.875

10000000 10000000 1.255

Monitor V

Bit Weights

Temperature Bit Weights

Temperature Conversion Example

Conversion Example

Monitor Conversion Example

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 21 22

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